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Dystrophin is the central protein of the dystrophin-glycoprotein complex (DGC) in skeletal and heart muscle cells. Dystrophin connects the actin cytoskeleton to the extracellular matrix (ECM). Severing the link between the ECM and the intracellular cytoskeleton has a devastating impact on the homeostasis of skeletal muscle cells, leading to a range of muscular dystrophies. In addition, the loss of a functional DGC leads to progressive dilated cardiomyopathy and premature death. Dystrophin functions as a molecular spring and the DGC plays a critical role in maintaining the integrity of the sarcolemma. Additionally, evidence is accumulating, linking the DGC to mechanosignalling, albeit this role is still less understood. This review article aims at providing an up-to-date perspective on the DGC and its role in mechanotransduction. We first discuss the intricate relationship between muscle cell mechanics and function, before examining the recent research for a role of the dystrophin glycoprotein complex in mechanotransduction and maintaining the biomechanical integrity of muscle cells. Finally, we review the current literature to map out how DGC signalling intersects with mechanical signalling pathways to highlight potential future points of intervention, especially with a focus on cardiomyopathies. A review of the function of the Dystrophic Glycoprotein Complex (DGC) in mechanosignaling provides an overview of the various components of DGC and potential mechanopathogenic mechanisms, particularly as they relate to muscular dystrophy. [ABSTRACT FROM AUTHOR]

Western rejections of paternalism as a practice of communication are informed by the analysis of John Stuart Mill in his classic work On Liberty. Mill asserted that the individual is best equipped to make moral judgments, over and above other systems of morality or traditions. The capacity to judge without paternalistic interference from the State is negative liberty. Mill advocated for a process grounded in robust communicative engagement as a method of self-cultivation. This requires active learning. Mill's analysis informs contemporary communication ethics with an emphasis on liberty as a virtue above faith in individuality, marking an influential contribution to the modern understanding of identity construction grounded in an originative "I" that must be protected. Libertarian and neoliberal accounts of ethics stand in Mill's shadow, extending his individualistic account of judgment. [ABSTRACT FROM AUTHOR]

The slow delayed-rectifier potassium current (IKs) is crucial for human cardiac action potential repolarization. The formation of IKs requires co-assembly of the KCNQ1 α-subunit and KCNE1 β-subunit, and mutations in either of these subunits can lead to hereditary long QT syndrome types 1 and 5, respectively. It is widely recognised that the KCNQ1/KCNE1 (Q1/E1) channel requires phosphatidylinositol-4,5-bisphosphate (PIP2) binding for function. We previously identified a cluster of basic residues in the proximal C-terminus of KCNQ1 that form a PIP2/phosphoinositide binding site. Upon charge neutralisation of these residues we found that the channel became more retained in the endoplasmic reticulum, which raised the possibility that channel–phosphoinositide interactions could play a role in channel trafficking. To explore this further we used a chemically induced dimerization (CID) system to selectively deplete PIP2 and/or phosphatidylinositol-4-phosphate (PI(4)P) at the plasma membrane (PM) or Golgi, and we subsequently monitored the effects on both channel trafficking and function. The depletion of PIP2 and/or PI(4)P at either the PM or Golgi did not alter channel cell-surface expression levels. However, channel function was extremely sensitive to the depletion of PIP2 at the PM, which is in contrast to the response of other cardiac potassium channels tested (Kir2.1 and Kv11.1). Surprisingly, when using the CID system IKs was dramatically reduced even before dimerization was induced, highlighting limitations regarding the utility of this system when studying processes highly sensitive to PIP2 depletion. In conclusion, we identify that the Q1/E1 channel does not require PIP2 or PI(4)P for anterograde trafficking, but is heavily reliant on PIP2 for channel function once at the PM. [ABSTRACT FROM AUTHOR]

Background: The heart rate (HR) response to exercise provides useful information about the autonomic function and has prognostic value, but its reproducibility over a long period of time, a critical requirement for using it as a clinical biomarker, is undetermined. Aim: To determine the intra-individual reproducibility of HR dynamics during sub-maximum exercise and one minute recovery. Methods: 1187 individuals from the Cardio physical fitness assessment test of the UK Biobank repeated a standard exercise stress test twice (recall time 34.2 ± 2.8 months) and were prospectively studied. Results: 821 individuals complied with inclusion criteria for reproducibility analysis, including peak workload differences between assessments ≤10 W. Intra-individual correlation between HR profile during the first and the second assessment was very high and higher than inter-individual correlation (0.92±0.08 vs 0.87±0.11, p<0.01). Intra-individual correlation of indices describing HR dynamics was: ρ = 0.81 for maximum HR during exercise; ρ = 0.71 for minimum HR during recovery; ρ = 0.70 for HR changes during both exercise and recovery; Intra-individual correlation was higher for these indices of HR dynamics than for resting HR (ρ = 0.64). Bland-Altman plots demonstrated good agreement between HR indices estimated during the first and second assessment. A small but consistent bias was registered for all repeated measurements. The intra-individual consistency of abnormal values was about 60–70%. Conclusions: The HR dynamics during exercise and recovery are reproducible over a period of 3 years, with moderate to strong intra-individual reproducibility of abnormal values. [ABSTRACT FROM AUTHOR]

The turn to populism in Western governments is increasingly marked by a breakdown in communication between those who disagree. Martin Buber's analysis of I-It as the nature of communication accounts for the impersonality and incivility of populist responses to globalisation. His writings on utopias account for the lack of centre in societies formed solely around bureaucratic means of production. This article elaborates upon his concept of I-It from I and Thou and his account of the breakdown of Marxism. These point to a loss of Thou as a binding and guiding force in community, leading to the uncivil distrust and populist reactions to globalisation. Neoliberal globalisation, as with the I-It interaction, is marked by a disconnection from nature in a system that is centred around self-interest. Buber theorised his Thou as the place where humanity is reconnected with nature and joined to others in dialogue. His work points to religious community as one witness to communities where forms of dialogue and interaction lie beyond market-based solution creation and negotiation. In Buber's work, a diagnosis for the anger and mistrust between neighbours and citizens in the present moment becomes salient: a disconnection from Thou as the organizing centre of community. [ABSTRACT FROM AUTHOR]

Long QT syndrome refers to a characteristic abnormality of the electrocardiogram and it is associated with a form of ventricular tachycardia known as torsadede-pointes and sudden arrhythmic death. It can occur as part of a hereditary syndrome or can be acquired usually because of drug administration. Here we review recent genetic, molecular and cellular discoveries and outline how they have furthered our understanding of this disease. Specifically we focus on compound mutations, genome wide association studies of QT interval, modifier genes and the therapeutic implications of this recent work. [ABSTRACT FROM AUTHOR]

Atrial fibrillation is the commonest cardiac arrhythmia and leads to significant clinical morbidity and mortality. It has a complex pathophysiology but is often initiated by atrial ectopic beats and because of atrial remodelling once it occurs it can become established. Thus therapeutic interventions designed to prevent the initial occurrence of the arrhythmia are particularly needed. At the cellular level, these ectopic beats arise because of abnormal calcium release events from the sarcoplasmic reticulum leading to an inward current mediated by the sodium-calcium exchanger. There has been considerable interest in this over the last few years largely focused on the ryanodine receptor and related signalling pathways. However, atrial myocytes also possess a well-developed inositol trisphosphate (IP 3 ) dependent calcium release system and this has been less studied. In this review we focus on pathways and molecules that couple via the G q\11 family of G-proteins including regulators of G-protein signalling that may influence IP 3 mediated calcium release and atrial fibrillation. [ABSTRACT FROM AUTHOR]

The study of family pedigrees with rare monogenic cardiovascular disorders has revealed new molecular players in physiological processes. Genome-wide association studies of complex traits with a heritable component may afford a similar and potentially intellectually richer opportunity. In this review we focus on the interpretation of genetic associations and the issue of causality in relation to known and potentially new physiology. We mainly discuss cardiometabolic traits as it reflects our personal interests, but the issues pertain broadly in many other disciplines. We also describe some of the resources that are now available that may expedite follow up of genetic association signals into observations on causal mechanisms and pathophysiology. [ABSTRACT FROM AUTHOR]

Connexins are essential in the propagation of electrical activity throughout the heart and are an important determinant of conduction velocity. Their dysfunction is an important factor in the genesis of abnormal cardiac rhythm and is relevant to the pathogenesis of a wide variety of cardiac pathologies. Here, we review the basic biology of connexins in the heart but particularly focus on their abnormal function in cardiac disease. [ABSTRACT FROM AUTHOR]

ATP-sensitive potassium channels ( KATP) are widely distributed and present in a number of tissues including muscle, pancreatic beta cells and the brain. Their activity is regulated by adenine nucleotides, characteristically being activated by falling ATP and rising ADP levels. Thus, they link cellular metabolism with membrane excitability. Recent studies using genetically modified mice and genomic studies in patients have implicated KATP channels in a number of physiological and pathological processes. In this review, we focus on their role in cellular function and protection particularly in the cardiovascular system. [ABSTRACT FROM AUTHOR]

Aims: ATP sensitive K+ channels (KATP) sense adenine nucleotide concentrations and thus couple the metabolic state of the cell to membrane potential. The hetero-octameric complex of a sulphonylurea receptor (SUR2B) and an inwardly rectifying K+ channel (Kir6.1) and the corresponding native channel in smooth muscle are relatively insensitive to variations in intracellular ATP. Activation of these channels in blood vessels during hypoxia/ischaemia is thought to be mediated via hormonal regulation such as cellular adenosine release or the release of mediators from the endothelium. In contrast, intracellular ATP prominently inhibits Kir6.2 containing complexes, such as those present in cardiac myocytes. Thus, we investigated differences in the mechanism of metabolic regulation of Kir6.1 and Kir6.2 containing KATP channels. [ABSTRACT FROM PUBLISHER]

Abstract: There is accumulating evidence that regulators of G-protein signalling (RGS) can have roles in signal transduction that are not related to GAP activity. Furthermore, RGSs have much more selective effects in vivo than might be anticipated from their behaviour in in vitro assays. I discuss the molecular mechanisms by which these phenomena might be explained including specific interactions between the RGS and G-protein coupled receptor, G-protein and effector. [Copyright &y& Elsevier]

Neutrophil leukocytes have a pivotal function in innate immunity. Dogma dictates that the lethal blow is delivered to microbes by reactive oxygen species (ROS) and halogens, products of the NADPH oxidase, whose impairment causes immunodeficiency. However, recent evidence indicates that the microbes might be killed by proteases, activated by the oxidase through the generation of a hypertonic, K+-rich and alkaline environment in the phagocytic vacuole. Here we show that K+ crosses the membrane through large-conductance Ca2+-activated K+ (BKCa) channels. Specific inhibitors of these channels, iberiotoxin and paxilline, blocked oxidase-induced 86Rb+ fluxes and alkalinization of the phagocytic vacuole, whereas NS1619, a BKCa channel opener, enhanced both. Characteristic outwardly rectifying K+ currents, reversibly inhibited by iberiotoxin, were demonstrated in neutrophils and eosinophils and the expression of the a-subunit of the BK channel was confirmed by western blotting. The channels were opened by the combination of membrane depolarization and elevated Ca2+ concentration, both consequences of oxidase activity. Remarkably, microbial killing and digestion were abolished when the BKCa channel was blocked, revealing an essential and unexpected function for this K+ channel in the microbicidal process. [ABSTRACT FROM AUTHOR]

1 We investigated the mechanism of action of two novel nonsulphonylurea ATP-sensitive potassium channel (K[SUBATP]) inhibitors, PNU-99963 and PNU-37883A, on four types of cloned K[SUBATP] channels. 2 Whole-cell currents were recorded in a symmetrical potassium (140 mM) gradient in HEK-293 cells stably expressing Kir6.2/SUR1, Kr6.2/SUR2A. Kr6.2/SUR2B or Kir6.1/SUP2B. 3 PNU-99963 potently inhibited the four K[SUBATP] channel clones. The concentration at which half-maximum current was inhibited (IC[SUB50]) was 66, 41, 43 and 11 nM for Kir6.2/SUR1, KR6.2/SUR2A, Kir6.2/SUR2B and Kir6.1/SUR2B, respectively. In contrast, PNU-99963 up to a concentration of 3μM had no significant effect on current generated in HEK-293 cells by transiently expressing Kir6.2Δ26, a C-terminal truncated pore-forming subunit of Kir6.2 4 PNU-37883A inhibited four types of K[SUBATP] channels, but to different extents. Inhibition of the putative smooth muscle K[SUBATP] channel types. Kir6.2/SUR2B (IC[SUB50]; 15 μM) and Kir6.1/SUR2B (IC[SUB50]; 6 μM), was significantly greater than inhibition of either the pancreatic β cell or cardiac K[SUBATP] channel clones. Moreover, PNU-37883A significantly inhibited currents generated by expressing Kir6.2Δ26 alone, with an IC[SUB50] of 5 μM, which was significantly increased to 38 μM when Kir6.2Δ26 was expressed with SUR2B. 5 In conclusion, two structurally different nonsulphonylurea compounds, PNU-99963 and PNU-37883A, inhibit K[SUBATP] channels via different mechanisms, namely through the sulphonylurea receptor (SUR), and the pore-forming subunits, respectively, although SUR2B reduced the inhibitory effects of PNU-37883A. While PNU-99963 potently inhibits all the four cloned K[SUBATP] channels, PNU-37883A has a degree of selectively towards both smooth muscle K[SUBATP] channels, but could not discriminate between them. [ABSTRACT FROM AUTHOR]

1. We investigated the mechanism of action of two novel nonsulphonylurea ATP-sensitive potassium channel (K(ATP)) inhibitors, PNU-99963 and PNU-37883A, on four types of cloned K(ATP) channels. 2. Whole-cell currents were recorded in a symmetrical potassium (140 mM) gradient in HEK-293 cells stably expressing Kir6.2/SUR1, Kir6.2/SUR2A, Kir6.2/SUR2B or Kir6.1/SUR2B. 3. PNU-99963 potently inhibited the four K(ATP) channel clones. The concentration at which half-maximum current was inhibited (IC(50)) was 66, 41, 43 and 11 nM for Kir6.2/SUR1, Kir6.2/SUR2A, Kir6.2/SUR2B and Kir6.1/SUR2B, respectively. In contrast, PNU-99963 up to a concentration of 3 microM had no significant effect on current generated in HEK-293 cells by transiently expressing Kir6.2Delta26, a C-terminal truncated pore-forming subunit of Kir6.2. 4. PNU-37883A inhibited four types of K(ATP) channels, but to different extents. Inhibition of the putative smooth muscle K(ATP) channel types, Kir6.2/SUR2B (IC(50); 15 microM) and Kir6.1/SUR2B (IC(50); 6 microM), was significantly greater than inhibition of either the pancreatic beta cell or cardiac K(ATP) channel clones. Moreover, PNU-37883A significantly inhibited currents generated by expressing Kir6.2Delta26 alone, with an IC(50) of 5 microM, which was significantly increased to 38 microM when Kir6.2Delta26 was expressed with SUR2B. 5. In conclusion, two structurally different nonsulphonylurea compounds, PNU-99963 and PNU-37883A, inhibit K(ATP) channels via different mechanisms, namely through the sulphonylurea receptor (SUR) and the pore-forming subunits, respectively, although SUR2B reduced the inhibitory effect of PNU-37883A. While PNU-99963 potently inhibits all the four cloned K(ATP) channels, PNU-37883A has a degree of selectivity towards both smooth muscle K(ATP) channels, but could not discriminate between them. [ABSTRACT FROM AUTHOR]

Examines the role of isoforms of pertussis toxin-sensitive G protein alpha subunits in coupling receptors to the G protein-gated inwardly rectifying potassium channel. Characterization of pertussis toxin-insensitive mutants; Delineating different patterns of receptor stimulation of channel activation.

Background and Purpose Experimental Approach Key Results Conclusion and Implications The canonical Kir6.2/SUR2A ventricular KATP channel is highly ATP‐sensitive and remains closed under normal physiological conditions. These channels activate only when prolonged metabolic compromise causes significant ATP depletion and then shortens the action potential to reduce contractile activity. Pharmacological activation of KATP channels is cardioprotective, but physiologically, it is difficult to understand how these channels protect the heart if they only open under extreme metabolic stress. The presence of a second KATP channel population could help explain this. Here, we characterise the biophysical and pharmacological behaviours of a constitutively active Kir6.1‐containing KATP channel in ventricular cardiomyocytes.Patch‐clamp recordings from rat ventricular myocytes in combination with well‐defined pharmacological modulators was used to characterise these newly identified K+ channels. Action potential recording, calcium (Fluo‐4) fluorescence measurements and video edge detection of contractile function were used to assess functional consequences of channel modulation.Our data show a ventricular K+ conductance whose biophysical characteristics and response to pharmacological modulation were consistent with Kir6.1‐containing channels. These Kir6.1‐containing channels lack the ATP‐sensitivity of the canonical channels and are constitutively active.We conclude there are two functionally distinct populations of ventricular KATP channels: constitutively active Kir6.1‐containing channels that play an important role in fine‐tuning the action potential and Kir6.2/SUR2A channels that activate with prolonged ischaemia to impart late‐stage protection against catastrophic ATP depletion. Further research is required to determine whether Kir6.1 is an overlooked target in Comprehensive in vitro Proarrhythmia Assay (CiPA) cardiac safety screens. [ABSTRACT FROM AUTHOR]

Studies the regions responsible for the assembly of inwardly rectifying potassium channels responsible for homo- and heteromultimerization. Characteristics; Role of region in the proximal c-terminus and transmembrane segment of M2 in determining assembly and compatibility; Identification of regions by biochemical and electrophysiological methods.

Identifies the mechanisms underlying altered ion handling after ryanodine binding to the sarcoplasmic reticulum calcium ion release channel protein. Characterization of single-channel conductance with representative members of three classes of permeant cation; Quantification of the change in single-channel conductance induced by ryanodine.

Examines the sarcoplasmic reticulum calcium ion-release channel in cardiac muscle cells. Role of the channel in cardiac muscle function; Provision of ligand-regulated pathway for the release of sequestered calcium ion; Initiation of contraction after cell excitation; Use of impermanent organic cation in biological channel; Factors affecting the conductance of ions.

Heart failure is a major clinical problem, with treatments involving medication, devices, and emerging neuromodulation therapies such as vagus nerve stimulation (VNS). Considering the ongoing interest in using VNS to treat cardiovascular disease, it is important to understand the genetic and molecular changes developing in the heart in response to this form of autonomic neuromodulation. This experimental animal (rat) study investigated the immediate transcriptional response of the ventricular myocardium to selective stimulation of vagal efferent activity using an optogenetic approach. Vagal preganglionic neurons in the dorsal motor nucleus of the vagus nerve were genetically targeted to express light-sensitive chimeric channelrhodopsin variant ChIEF and stimulated using light. RNA sequencing of the left ventricular myocardium identified 294 differentially expressed genes (false discovery rate < 0.05). Qiagen Ingenuity Pathway Analysis (IPA) highlighted 118 canonical pathways that were significantly modulated by vagal activity, of which 14 had a z score of (2/]2, including EIF-2, IL-2, integrin, and NFAT-regulated cardiac hypertrophy. IPA revealed the effect of efferent vagus stimulation on protein synthesis, autophagy, fibrosis, autonomic signaling, inflammation, and hypertrophy. IPA further predicted that the identified differentially expressed genes were the targets of 50 upstream regulators, including transcription factors (e.g., MYC and NRF1) and microRNAs (e.g., miR-335-3p and miR-338-3p). These data demonstrate that the vagus nerve has a major impact on the myocardial expression of genes involved in the regulation of key biological pathways. The transcriptional response of the ventricular myocardium induced by stimulation of vagal efferents is consistent with the beneficial effect of maintained/increased vagal activity on the heart. NEW & NOTEWORTHY This experimental animal study investigated the immediate transcriptional response of the ventricular myocardium to selective stimulation of vagal efferent activity. Vagal stimulation induced significant transcriptional changes in the heart involving the pathways controlling autonomic signaling, inflammation, fibrosis, and hypertrophy. This study provides the first direct evidence that myocardial gene expression is modulated by the activity of the autonomic nervous system. [ABSTRACT FROM AUTHOR]

BACKGROUND: The consequences of exercise-induced premature ventricular contractions (PVCs) in asymptomatic individuals remain unclear. This study aimed to assess the association between PVC burdens during submaximal exercise and major adverse cardiovascular events (MI/HF/LTVA: myocardial infarction [MI], heart failure [HF], and life-threatening ventricular arrhythmia [LTVA]), and all-cause mortality. Additional end points were MI, LTVA, HF, and cardiovascular mortality. METHODS: A neural network was developed to count PVCs from ECGs recorded during exercise (6 minutes) and recovery (1 minute) in 48 315 asymptomatic participants from UK Biobank. Associations were estimated using multivariable Cox proportional hazard models. Explorative studies were conducted in subgroups with cardiovascular magnetic resonance imaging data (n=6290) and NT-proBNP (N-terminal Pro-B-type natriuretic peptide) levels (n=4607) to examine whether PVC burden was associated with subclinical cardiomyopathy. RESULTS: Mean age was 56.8±8.2 years; 51.1% of the participants were female; and median follow-up was 12.6 years. Low PVC counts during exercise and recovery were both associated with MI/HF/LTVA risk, independently of clinical factors: adjusted hazard ratio (HR), 1.2 (1–5 exercise PVCs, P <0.001) and HR, 1.3 (1–5 recovery PVCs, P <0.001). Risks were higher with increasing PVC count: HR, 1.8 (>20 exercise PVCs, P <0.001) and HR, 1.6 (>5 recovery PVCs, P <0.001). A similar trend was observed for all-cause mortality, although associations were only significant for high PVC burdens: HRs, 1.6 (>20 exercise PVCs, P <0.001) and 1.5 (>5 recovery PVCs, P <0.001). Complex PVC rhythms were associated with higher risk compared with PVC count alone. PVCs were also associated with incident HF, LTVA, and cardiovascular mortality, but not MI. In the explorative studies, high PVC burden was associated with larger left ventricular volumes, lower ejection fraction, and higher levels of NT-proBNP compared with participants without PVCs. CONCLUSIONS: In this cohort of middle-aged and older adults, PVC count during submaximal exercise and recovery were both associated with MI/HF/LTVA, all-cause mortality, HF, LTVAs, and cardiovascular mortality, independent of clinical and exercise test factors, indicating an incremental increase in risk as PVC count rises. Complex PVC rhythms were associated with higher risk compared with PVC count alone. Underlying mechanisms may include the presence of subclinical cardiomyopathy. [ABSTRACT FROM AUTHOR]

Heart rate variability (HRV) is a cardiac autonomic marker with predictive value in cardiac patients. Ultra-short HRV (usHRV) can be measured at scale using standard and wearable ECGs, but its association with cardiovascular events in the general population is undetermined. We aimed to validate usHRV measured using ≤ 15-s ECGs (using RMSSD, SDSD and PHF indices) and investigate its association with atrial fibrillation, major adverse cardiac events, stroke and mortality in individuals without cardiovascular disease. In the National Survey for Health and Development (n = 1337 participants), agreement between 15-s and 6-min HRV, assessed with correlation analysis and Bland–Altman plots, was very good for RMSSD and SDSD and good for PHF. In the UK Biobank (n = 51,628 participants, 64% male, median age 58), after a median follow-up of 11.5 (11.4–11.7) years, incidence of outcomes ranged between 1.7% and 4.3%. Non-linear Cox regression analysis showed that reduced usHRV from 15-, 10- and 5-s ECGs was associated with all outcomes. Individuals with low usHRV (< 20th percentile) had hazard ratios for outcomes between 1.16 and 1.29, p < 0.05, with respect to the reference group. In conclusion, usHRV from ≤ 15-s ECGs correlates with standard short-term HRV and predicts increased risk of cardiovascular events in a large population-representative cohort. [ABSTRACT FROM AUTHOR]

Aims The brain controls the heart by dynamic recruitment and withdrawal of cardiac parasympathetic (vagal) and sympathetic activity. Autonomic control is essential for the development of cardiovascular responses during exercise, however, the patterns of changes in the activity of the two autonomic limbs, and their functional interactions in orchestrating physiological responses during exercise, are not fully understood. The aim of this study was to characterize changes in vagal parasympathetic drive in response to exercise and exercise training by directly recording the electrical activity of vagal preganglionic neurons in experimental animals (rats). Methods and results Single unit recordings were made using carbon-fibre microelectrodes from the populations of vagal preganglionic neurons of the nucleus ambiguus (NA) and the dorsal vagal motor nucleus of the brainstem. It was found that (i) vagal preganglionic neurons of the NA and the dorsal vagal motor nucleus are strongly activated during bouts of acute exercise, and (ii) exercise training markedly increases the resting activity of both populations of vagal preganglionic neurons and augments the excitatory responses of NA neurons during exercise. Conclusions These data show that central vagal drive increases during exercise and provide the first direct neurophysiological evidence that exercise training increases vagal tone. The data argue against the notion of exercise-induced central vagal withdrawal during exercise. We propose that robust increases in the activity of vagal preganglionic neurons during bouts of exercise underlie activity-dependent plasticity, leading to higher resting vagal tone that confers multiple health benefits associated with regular exercise. [ABSTRACT FROM AUTHOR]

Cardiac electrophysiology is regulated by the autonomic nervous system, and this has both pathophysiological, and possibly therapeutic importance. Furthermore, chamber differences in electrophysiology exist between atria and ventricles, yet there have been few direct comparisons. There is substantial literature on ion channel modulation at the single-cell level but less work on how this affects tissue-level parameters. We used a microelectrode array system to explore these issues using murine atrial and ventricular tissue slices. Activation time, conduction velocity and repolarisation were measured, and their modulation by temperature and pharmacological autonomic agonists were assessed. The system recorded reliable measurements under control conditions in the absence of drug/thermal challenge, and significant baseline differences were found in chamber electrophysiology. The sodium channel blocker mexiletine, produced large magnitude changes in all three measured parameters. Carbachol and isoprenaline induced differing effects in atria and ventricles, whereas temperature produced similar effects on activation and repolarisation. [ABSTRACT FROM AUTHOR]

Central to the genesis of ventricular cardiac arrhythmia are variations in determinants of excitability. These involve individual ionic channels and transporters in cardiac myocytes but also tissue factors such as variable conduction of the excitation wave, fibrosis and source-sink mismatch. It is also known that in certain diseases and particularly the channelopathies critical events occur with specific stressors. For example, in hereditary long QT syndrome due to mutations in KCNQ1 arrhythmic episodes are provoked by exercise and in particular swimming. Thus not only is the static substrate important but also how this is modified by dynamic signalling events associated with common physiological responses. In this review, we examine the regulation of ventricular excitability by signalling pathways from a cellular and tissue perspective in an effort to identify key processes, effectors and potential therapeutic approaches. We specifically focus on the autonomic nervous system and related signalling pathways. [ABSTRACT FROM AUTHOR]

We aimed to determine the pathophysiological impact of heart rate (HR) slowing on cardiac function. We have recently developed a murine model in which it is possible to conditionally delete the stimulatory heterotrimeric G-protein (Gαs) in the sinoatrial (SA) node after the addition of tamoxifen using cre-loxP technology. The addition of tamoxifen leads to bradycardia. We used this approach to examine the physiological and pathophysiological effects of HR slowing. We first looked at the impact on exercise performance by running the mice on a treadmill. After the addition of tamoxifen, mice with conditional deletion of Gαs in the SA node ran a shorter distance at a slower speed. Littermate controls preserved their exercise capacity after tamoxifen. Results consistent with impaired cardiac capacity in the mutants were also obtained with a dobutamine echocardiographic stress test. We then examined if HR reduction influenced pathological cardiac hypertrophy using two models: ligation of the left anterior descending coronary artery for myocardial infarction and abdominal aortic banding for hypertensive heart disease. In littermate controls, both procedures resulted in cardiac hypertrophy. However, induction of HR reduction prior to surgical intervention significantly ameliorated the hypertrophy. In order to assess potential protein kinase pathways that may be activated in the left ventricle by relative bradycardia, we used a phospho-antibody array and this revealed selective activation of phosphoinositide-3 kinase. In conclusion, HR reduction protects against pathological cardiac hypertrophy but limits physiological exercise capacity. Graphical Abstract [ABSTRACT FROM AUTHOR]

Mitochondrial dysfunction induced by acute cardiac ischemia–reperfusion (IR), may increase susceptibility to arrhythmias by perturbing energetics, oxidative stress production and calcium homeostasis. Although changes in mitochondrial morphology are known to impact on mitochondrial function, their role in cardiac arrhythmogenesis is not known. To assess action potential duration (APD) in cardiomyocytes from the Mitofusins-1/2 (Mfn1/Mfn2)-double-knockout (Mfn-DKO) compared to wild-type (WT) mice, optical-electrophysiology was conducted. To measure conduction velocity (CV) in atrial and ventricular tissue from the Mfn-DKO and WT mice, at both baseline and following simulated acute IR, multi-electrode array (MEA) was employed. Intracellular localization of connexin-43 (Cx43) at baseline was evaluated by immunohistochemistry, while Cx-43 phosphorylation was assessed by Western-blotting. Mfn-DKO cardiomyocytes demonstrated an increased APD. At baseline, CV was significantly lower in the left ventricle of the Mfn-DKO mice. CV decreased with simulated-ischemia and returned to baseline levels during simulated-reperfusion in WT but not in atria of Mfn-DKO mice. Mfn-DKO hearts displayed increased Cx43 lateralization, although phosphorylation of Cx43 at Ser-368 did not differ. In summary, Mfn-DKO mice have increased APD and reduced CV at baseline and impaired alterations in CV following cardiac IR. These findings were associated with increased Cx43 lateralization, suggesting that the mitofusins may impact on post-MI cardiac-arrhythmogenesis. [ABSTRACT FROM AUTHOR]

Mitochondrial dysfunction induced by acute cardiac ischemia–reperfusion (IR), may increase susceptibility to arrhythmias by perturbing energetics, oxidative stress production and calcium homeostasis. Although changes in mitochondrial morphology are known to impact on mitochondrial function, their role in cardiac arrhythmogenesis is not known. To assess action potential duration (APD) in cardiomyocytes from the Mitofusins-1/2 (Mfn1/Mfn2)-double-knockout (Mfn-DKO) compared to wild-type (WT) mice, optical-electrophysiology was conducted. To measure conduction velocity (CV) in atrial and ventricular tissue from the Mfn-DKO and WT mice, at both baseline and following simulated acute IR, multi-electrode array (MEA) was employed. Intracellular localization of connexin-43 (Cx43) at baseline was evaluated by immunohistochemistry, while Cx-43 phosphorylation was assessed by Western-blotting. Mfn-DKO cardiomyocytes demonstrated an increased APD. At baseline, CV was significantly lower in the left ventricle of the Mfn-DKO mice. CV decreased with simulated-ischemia and returned to baseline levels during simulated-reperfusion in WT but not in atria of Mfn-DKO mice. Mfn-DKO hearts displayed increased Cx43 lateralization, although phosphorylation of Cx43 at Ser-368 did not differ. In summary, Mfn-DKO mice have increased APD and reduced CV at baseline and impaired alterations in CV following cardiac IR. These findings were associated with increased Cx43 lateralization, suggesting that the mitofusins may impact on post-MI cardiac-arrhythmogenesis. [ABSTRACT FROM AUTHOR]

• Generation of an in vitro model of skeletal muscle using an isogenic pair of DMD patient-derived and CRISPR-corrected pluripotent stem cell (PSC) lines. • Analysis of myogenic transcriptomes identified dysregulated genes in DMD, including those required for excitation-contraction coupling and muscle contraction. • Analysis of intracellular Ca2+ transients and mathematical modeling of Ca2+ dynamics reveal significantly reduced cytosolic Ca2+ clearance rates in DMD-PSC derived myotubes • A human-relevant in vitro platform with functional assays enables rapid pre-clinical assessment of potential therapies for treating DMD. Mutations in the dystrophin gene cause the most common and currently incurable Duchenne muscular dystrophy (DMD) characterized by progressive muscle wasting. Although abnormal Ca2+ handling is a pathological feature of DMD, mechanisms underlying defective Ca2+ homeostasis remain unclear. Here we generate a novel DMD patient-derived pluripotent stem cell (PSC) model of skeletal muscle with an isogenic control using clustered regularly interspaced short palindromic repeat (CRISPR)-mediated precise gene correction. Transcriptome analysis identifies dysregulated gene sets in the absence of dystrophin, including genes involved in Ca2+ handling, excitation-contraction coupling and muscle contraction. Specifically, analysis of intracellular Ca2+ transients and mathematical modeling of Ca2+ dynamics reveal significantly reduced cytosolic Ca2+ clearance rates in DMD-PSC derived myotubes. Pharmacological assays demonstrate Ca2+ flux in myotubes is determined by both intracellular and extracellular sources. DMD-PSC derived myotubes display significantly reduced velocity of contractility. Compared with a non-isogenic wildtype PSC line, these pathophysiological defects could be rescued by CRISPR-mediated precise gene correction. Our study provides new insights into abnormal Ca2+ homeostasis in DMD and suggests that Ca2+ signaling pathways amenable to pharmacological modulation are potential therapeutic targets. Importantly, we have established a human physiology-relevant in vitro model enabling rapid pre-clinical testing of potential therapies for DMD. [ABSTRACT FROM AUTHOR]

A correction to the article "The large-conductance Ca2+ -activated K+ channel is essential for innate immunity" that was published in the 2004 issue is presented.

Background: Opening of KATP channels by systemic levcromakalim treatment triggers attacks in migraine patients and hypersensitivity to von Frey stimulation in a mouse model. Blocking of these channels is effective in several preclinical migraine models. It is unknown in what tissue and cell type KATP-induced migraine attacks are initiated and which KATP channel subtype is targeted.Methods: In mouse models, we administered levcromakalim intracerebroventricularly, intraperitoneally and intraplantarily and compared the nociceptive responses by von Frey and hotplate tests. Mice with a conditional loss-of-function mutation in the smooth muscle KATP channel subunit Kir6.1 were given levcromakalim and GTN and examined with von Frey filaments. Arteries were tested for their ability to dilate ex vivo. mRNA expression, western blotting and immunohistochemical stainings were made to identify relevant target tissue for migraine induced by KATP channel opening.Results: Systemic administration of levcromakalim induced hypersensitivity but central and local administration provided antinociception respectively no effect. The Kir6.1 smooth muscle knockout mouse was protected from both GTN and levcromakalim induced hypersensitivity, and their arteries had impaired dilatory response to the latter. mRNA and protein expression studies showed that trigeminal ganglia did not have significant KATP channel expression of any subtype, whereas brain arteries and dura mater primarily expressed the Kir6.1 + SUR2B subtype.Conclusion: Hypersensitivity provoked by GTN and levcromakalim in mice is dependent on functional smooth muscle KATP channels of extracerebral origin. These results suggest a vascular contribution to hypersensitivity induced by migraine triggers. [ABSTRACT FROM AUTHOR]

In atrial and nodal cardiac myocytes, M2 muscarinic receptors activate inhibitory G-proteins (Gi/o), which in turn stimulate G-protein-gated inwardly rectifying K+ channels through direct binding of the G/3y subunit. Despite also releasing Gβγ, Gs-coupled receptors such as the β-adrenergic receptor are not able to prominently activate this current. An appealing hypothesis would be if components were sequestered in membrane domains such as caveolae/rafts. Using biochemical fractionation followed by Western blotting and/or radioligand binding experiments, we examined the distribution of the components in stable HEK293 and HL-I cells, which natively express the transduction cascade. The channel, M2 muscarinic, and A1 adenosine receptors were located in noncaveolar/nonraft fractions. Giα12 was enriched in both caveolar/raft and noncaveolar/ nonraft fractions. In contrast, Gsα was only enriched in caveolar/raft fractions. We constructed YFP-tagged caveolin-2 (YFP-Cav2) and chimeras with the M2 (M2-YFP-Cav2) and A1 (A1-YFP-Cav2) receptors. Analysis of gradient fractions showed that these receptor chimeras were now localized to caveolae-enriched fractions. Microscopy showed that M2-YFP and A1-YFP had a diffuse homogenous membrane signal. YFPCav2, M2-YFP-Cav2, and A1-YFP-Cav2 revealed a more punctuate pattern. Finally, we looked at the consequences for signaling. Activation via M2-YFP-Cav2 or A1-YFP-Cav2 revealed substantially slower kinetics compared with M2-YFP or A1-YFP and was reversed by the addition of methyl-β-cyclodextrin. Thus the localization of the channel signal transduction cascade in non-cholesterol rich domains substantially enhances the speed of signaling. The presence of Gsα solely in caveolae may account for signaling selectivity between Gi/o and Gs-coupled receptors. [ABSTRACT FROM AUTHOR]

An inwardly rectifying K+ current is present in atrial cardiac myocytes that is activated by acetylcholine (IKACh). Physiologically, activation of the current in the SA node is important in slowing the heart rate with increased parasympathetic tone. It is a paradigm for the direct regulation of signaling effectors by the Gβγ G-protein subunit. Many questions have been addressed in heterologous expression systems with less focus on the behaviour in native myocytes partly because of the technical difficulties in undertaking comparable studies in native cells. In this study, we characterise a potassium current in the atrial-derived cell line HL-1. Using an electrophysiological approach, we compare the characteristics of the potassium current with those in native atrial cells and in a HEK cell line expressing the cloned Kir3.1/3.4 channel. The potassium current recorded in HL-1 is inwardly rectifying and activated by the muscarinic agonist carbachol. Carbachol-activated currents were inhibited by pertussis toxin and tertiapin-Q. The basal current was time-dependently increased when GTP was substituted in the patch-clamp pipette by the non-hydrolysable analogue GTPγS. We compared the kinetics of current modulation in HL-1 with those of freshly isolated atrial mouse cardiomyocytes. The current activation and deactivation kinetics in HL-1 cells are comparable to those measured in atrial cardiomyocytes. Using immunofluorescence, we found GIRK4 at the membrane in HL-1 cells. Real-time RT-PCR confirms the presence of mRNA for the main G-protein subunits, as well as for M2 muscarinic and A1 adenosine receptors. The data suggest HL-1 cells are a good model to study IKAch. [ABSTRACT FROM AUTHOR]

Multiple isoforms of inhibitory Gα-subunits (Gαi1,2,3, as well as Gα0) are present within the heart, and their role in modulating pacemaker function remains unresolved. Do inhibitory Gα-subunits selectively modulate parasympathetic heart rate responses? Published findings using a variety of experimental approaches have implicated roles for Gαi2, Gαi3, and Gα0 in parasympathetic signal transduction. We have compared in vivo different groups of mice with global genetic deletion of Giα1/Gαi3, Gαi2, and Gα0 against littermate controls using implanted ECG telemetry. Significant resting tachycardia was observed in Gαi2-/- and Gα0-/- mice compared with control and Gαi1-/- /Gαi3-/- mice (P < 0.05). Loss of diurnal heart rate variation was seen exclusively in Gα0-/- mice. Using heart rate variability (HRV) analysis, compared with littermate controls (4.02 ms² ± 1.17; n = 6, Gαi2-/-) mice have a selective attenuation of high-frequency (HF) power (0.73 ms² ± 0.31; n = 5, P < 0.05). Gαi1-/- /Gαi3-/- and Gα0-/- cohorts have nonsignificant changes in HF power. Gα0-/- mice have a different basal HRV signature. The observed HRV phenotype in Gαi2-/- mice was qualitatively similar to atropine (1 mg/kg)-treated controls [and mice treated with the GIRK channel blocker tertiapinQ (0.05 mg/kg)]. Maximal cardioinhibitory response to the M2-receptor agonist carbachol (0.5 mg/kg) compared with basal heart rate was attenuated in Gαi2-/- mice (0.08 ± 0.04; n = 6) compared to control (0.27 ± 0.04; n = 7 P < 0.05). Our data suggest a selective defect of parasympathetic heart rate modulation in mice with Gαi2 deletion. Mice with Gα0 deletion also have a defect in short-term heart rate dynamics, but this is qualitatively different to the effects of atropine, tertiapinQ, and Gαi2 deletion. In contrast, Gαi1 and Gαi3 do not appear to be essential for parasympathetic responses in vivo. [ABSTRACT FROM AUTHOR]

Phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) is a key component in signal transduction, being a precursor to other signalling molecules and itself associated with roles in signal transduction and cell biology. Tubby is a membrane bound transcription factor whose dysfunction results in obesity in mice. It contains a domain that selectively binds PtdIns(4,5)P2. We have investigated the use of a fluorescently tagged version of this domain to monitor changes in PtdIns(4,5)P2 concentration in living cells and compared it to the pleckstrin homology domain of PLCδ1. Our results show that selected mutants of this domain report receptor-mediated changes in cellular PtdIns(4,5)P2. In contrast to the pleckstrin homology domain of PLCδ1 it does not have a significant affinity for inositol 1,4,5-trisphosphate (IP3). Using a selected mutant, we examine the regulation of ATP-sensitive K+ channels via a Gq/11-coupled receptor. These experiments reveal a correlation between reporter translocation and the onset of current inhibition whilst the recovery of current after agonist removal is delayed when compared to the reporter. Furthermore our studies reveal the importance of Ca2+ in determining the overall activity of phospholipase C in living cells. This probe may be valuable in examining changes in PtdIns(4,5)P2 distinct from those of IP3 in intact cells in a variety of physiological settings. [ABSTRACT FROM AUTHOR]

The open state of M(Kv7.2/7.3) potassium channels is maintained by membrane phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2). They can be closed on stimulating receptors that induce PI(4,5)P2 hydrolysis. In sympathetic neurons, closure induced by stimulating M1-muscarinic acetylcholine receptors (mAChRs) has been attributed to depletion of PI(4,5)P2, whereas closure by bradykinin B2-receptors (B2-BKRs) appears to result from formation of IP3 and release of Ca2+, implying that BKR stimulation does not deplete PI(4,5)P2. We have used a fluorescently tagged PI(4,5)P2-binding construct, the C-domain of the protein tubby, mutated to increase sensitivity to PI(4,5)P2 changes (tubby-R332H-cYFP), to provide an on-line read-out of PI(4,5)P2 changes in single living sympathetic neurons after receptor stimulation. We find that the mAChR agonist, oxotremorine-M (oxo-M), produces a near-complete translocation of tubby-R332H-cYFP into the cytoplasm, whereas bradykinin (BK) produced about one third as much translocation. However, translocation by BK was increased to equal that produced by oxo-M when synthesis of PI(4,5)P2 was inhibited by wortmannin. Further, wortmannin ‘rescued’ M-current inhibition by BK after Ca2+-dependent inhibition was reduced by thapsigargin. These results provide the first direct support for the view that BK accelerates PI(4,5)P2 synthesis in these neurons, and show that the mechanism of BKR-induced inhibition can be switched from Ca2+ dependent to PI(4,5)P2 dependent when PI(4,5)P2 synthesis is inhibited. [ABSTRACT FROM AUTHOR]

Strong inwardly rectifying K(+) (K(IR)) channels that contribute to maintaining the resting membrane potential are encoded by the Kir2.0 family (Kir2.1-2.4). In smooth muscle, K(IR) currents reported so far have the characteristics of Kir2.1. However, Kir2.4, which exhibits unique characteristics of barium block, has been largely overlooked. Using patch-clamp techniques, we characterized K(IR) channels in cultured human pulmonary artery smooth muscle (HPASM) cells and compared them to cloned Kir2.1 and Kir2.4 channels. In a physiological K(+) gradient, inwardly rectifying currents were observed in HPASM cells, the magnitude and reversal potential of which were sensitive to extracellular K(+) concentration. Ba(2+) (100 microM ) significantly inhibited inward currents and depolarized HPASM cells by approximately 10 mV. In 60 mM extracellular K(+), Ba(2+) blocked K(IR) currents in HPASM cells with a 50% inhibitory concentration of 39.1 microM at -100 mV compared to 3.9 microM and 65.6 microM for Kir2.1 and Kir2.4, respectively. Cloned Kir2.4 and K(IR) currents in HPASM cells showed little voltage dependence to Ba(2+) inhibition, which blocked at a more superficial site than for Kir2.1. Single-channel recordings revealed strong inwardly rectifying channels with an average conductance of 21 pS in HPASM cells, not significantly different from either Kir2.1 (19.6 pS) or Kir2.4 (19.4 pS). Reverse-transcription polymerase chain reaction detected products corresponding to Kir2.1, Kir2.2 and Kir2.4 but not Kir2.3. We demonstrate that cultured HPASM cells express K(IR) channels and suggest both Kir2.1 and Kir2.4 subunits contribute to these channels, although the whole-cell current characteristics described share more similarity with Kir2.4. [ABSTRACT FROM AUTHOR]

Using fluorescence resonance energy transfer (FRET) microscopy, we investigate how heterotrimeric G proteins interact with G protein-coupled receptors (GPCRs). In the absence of receptor activation, the α2A adrenergic and muscarinic M4 receptors are present on the cell membrane as dimers. Furthermore, there is an interaction between the G protein subunits two, β1, and γ2 and a number of GPCRs including M4, α2A, the adenosine Al receptor, and the dopamine D2 receptor under resting conditions. The interaction between GPCRs and Gα proteins shows specificity: there is interaction between the α2A receptor and Go, but little interaction between the α2A receptor and Gs. In contrast, the predominantly Gs-coupled prostacyclin receptor interacted with Gs, but there was little interaction between the prostacyclin receptor and Go. Inverse agonists did not change the FRET ratio, whereas the addition of agonist resulted in a modest fall. Our work suggests that GPCR dimers and the G protein heterotrimer are present at the cell membrane in the resting state in a pentameric complex. [ABSTRACT FROM AUTHOR]

G protein-gated inwardly rectifying K[sup +] (Kir) channels are found in neurones, atrial myocytes, and endocrine cells and are involved in generating late inhibitory postsynaptic potentials, slowing the heart rate and inhibiting hormone release. They are activated by G proteincoupled receptors (GPCRs) via the inhibitory family of G protein, G[sub i/o], in a membrane-delimited fashion by the direct binding of Gβγ dimers to the channel complex. In this study we are concerned with the kinetics of deactivation of the cloned neuronal G protein-gated K[sup +] channel, Kir3.1 + 3.2A, after stimulation of a number of GPCRs. Termination of the channel activity on agonist removal is thought to solely depend on the intrinsic hydrolysis rate of the G protein α subunit. In this study we present data that illustrate a more complex behavior. We hypothesize that there are two processes that account for channel deactivation: agonist unbinding from the GPCR and GTP hydrolysis by the G protein α subunit. With some combinations of agonist/GPCR, the rate of agonist unbinding is slow and rate-limiting, and deactivation kinetics are not modulated by regulators of G protein-signaling proteins. In another group, channel deactivation is generally faster and limited by the hydrolysis rate of the G protein α subunit. G protein isoform and interaction with G protein-signaling proteins play a significant role with this group of GPCRs. [ABSTRACT FROM AUTHOR]

ATP-sensitive K+ channels are an octameric assembly of two proteins, a sulfonylurea receptor (SUR1) and an ion conducting subunit (Kir 6.0). We have examined the role of the C-terminus of SUR1 by expressing a series of truncation mutants together with Kir6.2 stably in HEK293 cells. Biochemical analyses using coimmunoprecipitation indicate that SUR1 deletion mutants and Kir6.2 assemble and that a SUR1 deletion mutant binds glibenclamide with high affinity. Electrophysiological recordings indicate that ATP sensitivity is normal but the response of the mutant channel complexes to tolbutamide, MgADP and diazoxide is disturbed. Quantitative immunofluorescence and cell surface biotinylation supports the idea that there is little disturbance in the efficiency of trafficking. Our data show that deletions of the C-terminal most cytoplasmic domain of SUR1, can result in functional channels at the plasma membrane in mammalian cells that have an abnormal response to physiological and pharmacological agents. [ABSTRACT FROM AUTHOR]

The electrocardiogram (ECG) is a commonly used clinical tool that reflects cardiac excitability and disease. Many parameters are can be measured and with the improvement of methodology can now be quantified in an automated fashion, with accuracy and at scale. Furthermore, these measurements can be heritable and thus genome wide association studies inform the underpinning biological mechanisms. In this review we describe how we have used the resources in UK Biobank to undertake such work. In particular, we focus on a substudy uniquely describing the response to exercise performed at scale with accompanying genetic information. [ABSTRACT FROM AUTHOR]

We have assessed the role of ric-b8 in the control of heart rate after the gene was implicated in a recent genome-wide association study of resting heart rate. We developed a novel murine model in which it was possible to conditionally delete ric-8b in the sinoatrial (SA) node after the addition of tamoxifen. Despite this, we were unable to obtain homozygotes and thus studied heterozygotes. Haploinsufficiency of ric-8b in the sinoatrial node induced by the addition of tamoxifen in adult animals leads to mice with a reduced heart rate. However, other electrocardiographic intervals (e.g., PR and QRS) were normal, and there was no apparent arrhythmia such as heart block. The positive chronotropic response to isoprenaline was abrogated, whereas the response to carbachol was unchanged. The pacemaker current If (funny current) has an important role in regulating heart rate, and its function is modulated by both isoprenaline and carbachol. Using a heterologous system expressing HCN4, we show that ric-8b can modulate the HCN4 current. Overexpression of ric-8b led to larger HCN4 currents, whereas silencing ric-8b led to smaller currents. Ric-8b modulates heart rate responses in vivo likely via its actions on the stimulatory G-protein. [ABSTRACT FROM AUTHOR]

KATP channels in the vasculature composed of Kir6.1 regulate vascular tone and may contribute to the pathogenesis of endotoxemia. We used mice with cell-specific deletion of Kir6.1 in smooth muscle (smKO) and endothelium (eKO) to investigate this question. We found that smKO mice had a significant survival disadvantage compared with their littermate controls when treated with a sub-lethal dose of lipopolysaccharide (LPS). All cohorts of mice became hypotensive following bacterial LPS administration; however, mean arterial pressure in WT mice recovered to normal levels, whereas smKO struggled to overcome LPS-induced hypotension. In vivo and ex vivo investigations revealed pronounced cardiac dysfunction in LPS-treated smKO, but not in eKO mice. Similar results were observed in a cecal slurry injection model. Metabolomic profiling of hearts revealed significantly reduced levels of metabolites involved in redox/energetics, TCA cycle, lipid/fatty acid and amino acid metabolism. Vascular smooth muscle-localised KATP channels have a critical role in the response to systemic infection by normalising cardiac function and haemodynamics through metabolic homeostasis. Key messages: • Mice lacking vascular KATP channels are more susceptible to death from infection. • Absence of smooth muscle KATP channels depresses cardiac function during infection. • Cardiac dysfunction is accompanied by profound changes in cellular metabolites. • Findings from this study suggest a protective role for vascular KATP channels in response to systemic infection. [ABSTRACT FROM AUTHOR]

Sudden cardiac death is responsible for half of all deaths from cardiovascular disease. The analysis of the electrophysiological substrate for arrhythmias is crucial for optimal risk stratification. A prolonged T-peak-to-Tend (Tpe) interval on the electrocardiogram is an independent predictor of increased arrhythmic risk, and Tpe changes with heart rate are even stronger predictors. However, our understanding of the electrophysiological mechanisms supporting these risk factors is limited. We conducted genome-wide association studies (GWASs) for resting Tpe and Tpe response to exercise and recovery in ∼30,000 individuals, followed by replication in independent samples (∼42,000 for resting Tpe and ∼22,000 for Tpe response to exercise and recovery), all from UK Biobank. Fifteen and one single-nucleotide variants for resting Tpe and Tpe response to exercise, respectively, were formally replicated. In a full dataset GWAS, 13 further loci for resting Tpe, 1 for Tpe response to exercise and 1 for Tpe response to exercise were genome-wide significant (p ≤ 5 × 10−8). Sex-specific analyses indicated seven additional loci. In total, we identify 32 loci for resting Tpe, 3 for Tpe response to exercise and 3 for Tpe response to recovery modulating ventricular repolarization, as well as cardiac conduction and contraction. Our findings shed light on the genetic basis of resting Tpe and Tpe response to exercise and recovery, unveiling plausible candidate genes and biological mechanisms underlying ventricular excitability. [ABSTRACT FROM AUTHOR]

KIR6.1 (KCNJ8) is a subunit of ATP sensitive potassium channel (KATP) that plays an important role in the control of peripheral vascular tone and is highly expressed in brain contractile cells (vascular smooth muscle cells and pericytes). This study determined the effect of global deletion of the KIR6.1 subunit on cerebral blood flow, neurovascular coupling and cerebral oxygenation in mice. In KIR6.1 deficient mice resting cerebral blood flow and brain parenchymal partial pressure of oxygen (P O2) were found to be markedly lower compared to that in their wildtype littermates. However, cortical blood oxygen level dependent responses triggered by visual stimuli were not affected in conditions of KIR6.1 deficiency. These data suggest that KATP channels containing KIR6.1 subunit are critically important for the maintenance of normal cerebral perfusion and parenchymal P O2 but play no significant role in the mechanisms underlying functional changes in brain blood flow. [ABSTRACT FROM AUTHOR]

A murine line haploinsufficient in the cardiac sodium channel has been used to model human Brugada syndrome: a disease causing sudden cardiac death due to lethal ventricular arrhythmias. We explored the effects of cholinergic tone on electrophysiological parameters in wild-type and genetically modified, heterozygous, Scn5a+/- knockout mice. Scn5a+/- ventricular slices showed longer refractory periods than wild-type both at baseline and during isoprenaline challenge. Scn5a+/- hearts also showed lower conduction velocities and increased mean increase in delay than did littermate controls at baseline and blunted responses to isoprenaline challenge. Carbachol exerted limited effects but reversed the effects of isoprenaline with coapplication. Scn5a+/- mice showed a reduction in conduction reserve in that isoprenaline no longer increased conduction velocity, and this was not antagonized by muscarinic agonists. [ABSTRACT FROM AUTHOR]