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Aims The concept of "atrial cardiomyopathy" (AtCM) had been percolating through the literature since its first mention in 1972. Since then, publications using the term were sporadic until the decision was made to convene an expert working group with representation from four multinational arrhythmia organizations to prepare a consensus document on atrial cardiomyopathy in 2016 (EHRA/HRS/APHRS/SOLAECE expert consensus on atrial cardiomyopathies: definition, characterization, and clinical implication). Subsequently, publications on AtCM have increased progressively. Methods and results The present consensus document elaborates the 2016 AtCM document further to implement a simple AtCM staging system (AtCM stages 1–3) by integrating biomarkers, atrial geometry, and electrophysiological changes. However, the proposed AtCM staging needs clinical validation. Importantly, it is clearly stated that the presence of AtCM might serve as a substrate for the development of atrial fibrillation (AF) and AF may accelerates AtCM substantially, but AtCM per se needs to be viewed as a separate entity. Conclusion Thus, the present document serves as a clinical consensus statement of the European Heart Rhythm Association (EHRA) of the ESC, the Heart Rhythm Society (HRS), the Asian Pacific Heart Rhythm Society (APHRS), and the Latin American Heart Rhythm Society (LAHRS) to contribute to the evolution of the AtCM concept. [ABSTRACT FROM AUTHOR]

Arterial cardiovascular events are the leading cause of death in patients with [JAK2.sup.V617F] myeloproliferative neoplasms (MPNs). However, their mechanisms are poorly understood. The high prevalence of myocardial infarction without significant coronary stenosis or atherosclerosis in patients with MPNs suggests that vascular function is altered. The consequences of [JAK2.sup.V617F] mutation on vascular reactivity are unknown. We observe here increased responses to vasoconstrictors in arteries from [Jak2.sup.V617F] mice resulting from a disturbed endothelial NO pathway and increased endothelial oxidative stress. This response was reproduced in WT mice by circulating microvesicles isolated from patients carrying [JAK2.sup.V617F] and by erythrocyte-derived microvesicles from transgenic mice. Microvesicles of other cellular origins had no effect. This effect was observed ex vivo on isolated aortas, but also in vivo on femoral arteries. Proteomic analysis of microvesicles derived from [JAK2.sup.V617F] erythrocytes identified increased expression of myeloperoxidase as the likely mechanism accounting for their effect. Myeloperoxidase inhibition in microvesicles derived from [JAK2.sup.V617F] erythrocytes suppressed their effect on oxidative stress. Antioxidants such as simvastatin and W-acetyl cysteine improved arterial dysfunction in [Jak2.sup.V617F] mice. In conclusion, [JAK2.sup.V617F] MPNs are characterized by exacerbated vasoconstrictor responses resulting from increased endothelial oxidative stress caused by circulating erythrocyte-derived microvesicles. Simvastatin appears to be a promising therapeutic strategy in this setting., Introduction Bcr/Abl-negative myeloproliferative neoplasms (MPNs) are clonal hematopoietic stem cell disorders characterized by the proliferation of particular hematopoietic lineages without blockage in cell maturation. They include polycythemia vera, essential thrombocythemia, [...]

The transfection of cardiac myocytes is difficult, and so most of the data regarding the regulation of trafficking and targeting of cardiac ion channels have been obtained using heterologous expression systems. Here we apply the fast biolistic transfection procedure to adult cardiomyocytes to show that biolistically introduced exogenous voltage-gated potassium channel, Kv1.5, is functional and, like endogenous Kv1.5, localizes to the intercalated disc, where it is expressed at the surface of that structure. Transfection efficiency averages 28.2 [+ or -] 5.7% of surviving myocytes at 24 h postbombardment. Ventricular myocytes transfected with a tagged Kv1.5 exhibit an increased sustained current component that is ~40% sensitive to 100 [micro]M 4-aminopyridine and which is absent in myocytes transfected with a fluorescent protein-encoding construct alone. Kv1.5 deletion mutations known to reduce the surface expression of the channel in heterologous cells similarly reduce the surface expression in transfected ventricular myocytes, although targeting to the intercalated disc per se is generally unaffected by both N[H.sub.2]- and COOH-terminal deletion mutants. Expressed current levels in wild-type Kvl.5, Kvl.5[DELTA]SH3(1), Kvl.5[DELTA]N209, and Kvl.5[DELTA]N135 mutants were well correlated with apparent surface expression of the channel at the intercalated disc. Our results conclusively demonstrate functionality of channels present at the intercalated disc in native myocytes and identify determinants of trafficking and surface targeting in intact cells. Clearly, biolistic transfection of adult cardiac myocytes will be a valuable method to study the regulation of surface expression of channels in their native environment. cardiomyocyte; transfection; potassium channel doi: 10.1152/ajpcell.00005.2010.

The second messengers cAMP and cGMP can be degraded by specific members of the phosphodiesterase superfamily or by active efflux transporters, namely the multidrug resistance-associated proteins (MRPs) MRP4 and MRP5. To determine the role of MRP4 and MRP5 in cell signaling, we studied arterial SMCs, in which the effects of cyclic nucleotide levels on SMC proliferation have been well established. We found that MRP4, but not MRP5, was upregulated during proliferation of isolated human coronary artery SMCs and following injury of rat carotid arteries in vivo. MRP4 inhibition significantly increased intracellular cAMP and cGMP levels and was sufficient to block proliferation and to prevent neointimal growth in injured rat carotid arteries. The antiproliferative effect of MRP 4 inhibition was related to PKA/CREB pathway activation. Here we provide what we believe to be the first evidence that MRP4 acts as an independent endogenous regulator of intracellular cyclic nucleotide levels and as a mediator of cAMP-dependent signal transduction to the nucleus. We also identify MRP4 inhibition as a potentially new way of preventing abnormal VSMC proliferation., Introduction cAMP and cGMP are second messengers that relay external signals to downstream effector proteins. The most common targets are cAMP-dependent PKA and cGMP-dependent PKG, which regulate a large number [...]

Membrane-associated guanylate kinase proteins (MAGUKs) are important determinants of localization and organization of ion channels into specific plasma membrane domains. However, their exact role in channel function and cardiac excitability is not known. We examined the effect of synapse-associated protein 97 (SAP97), a MAGUK abundantly expressed in the heart, on the function and localization of Kv1.5 subunits in cardiac myocytes. Recombinant SAP97 or Kv1.5 subunits tagged with green fluorescent protein (GFP) were over-expressed in rat neonatal cardiac myocytes and in Chinese hamster ovary (CHO) cells from adenoviral or plasmidic vectors. Immunocytochemistry, fluorescence recovery after photobleaching, and patchclamp techniques were used to study the effects of SAP97 on the localization, mobility, and function of Kv1.5 subunits. Adenovirus-mediated SAP97 overexpression in cardiac myocytes resulted in the clustering of endogenous Kv1.5 subunits at myocyte-myocyte contacts and an increase in both the maintained component of the outward [K.sup.+] current, [I.sub.Kur] (5.64 [+ or -] 0.57 pA/pF in SAP97 myocytes vs. 3.23 [+ or -] 0.43 pA/pF in controls) and the number of 4-aminopyridine-sensitive potassium channels in cell-attached membrane patches. In live myocytes, GFP-Kv1.5 subunits were mobile and organized in clusters at the basal plasma membrane, whereas SAP97 overexpression reduced their mobility. In CHO cells, Kvl.5 channels were diffusely distributed throughout the cell body and freely mobile. When coexpressed with SAP97, Kv subunits were organized in plaquelike clusters and poorly mobile. In conclusion, SAP97 regulates the [K.sup.+] current in cardiac myocytes by retaining and immobilizing Kv1.5 subunits in the plasma membrane. This new regulatory mechanism may contribute to the targeting of Kv channels in cardiac myocytes. potassium channel; membrane-associated guanylate kinase proteins; fluorescence recovery after photobleaching

The behavior of voltage-activated outward K+ current components was analyzed during the serum-stimulated growth of cultured human atrial myocytes. The density of the rapidly inactivating component (Ito,1) of the K+ current decreased more rapidly than the density of the slowly inactivating component in chronically overloaded atrial myocytes. A decrease in the rate of inactivation and recovery from inactivation of Ito,1 was also detected during the serum-induced growth of human atrial myocytes.

The sodium/calcium (Na+/Ca2+) exchangers play an important role in the regulation of ion conductances in mammalian cells. In human atrial myocytes, these exchangers have been shown to participate in the generation of cardiac action potential plateau. Herein, whole cell patch-clamp recordings of human heart cells show that Na+/Ca2+ exchange contribute to the electrical activity of human atrial myocytes by contributing to the development of action potentials.

The characteristic features of calcium ion signalling in fura 2-loaded whole cell clamped myocytes is determined. The myocytes are obtained from samples of human atrial appendages of 3 day to4 year old children. The characteristic features reveral that the release of calcium ions from the sarcoplasmic reticulum regulates the signalling of contraction in early postuatal myocytes.

The effects of endothelin-1 (ET-1) on the L-type [Ca.sup.2+] current ([I.sub.Ca]) were examined in whole cell patch-clamped human atrial myocytes. Depending on the initial current density, ET-1 (10 nM) increased the amplitude of [I.sub.Ca] by 99 [+ or -] 7% or decreased it by 33 [+ or -] 2%. The stimulatory effect predominated on current of low density (2.3 [+ or -] 0.2 pA/pF), whereas [I.sub.Ca] of higher density (5.8 [+ or -] 0.3 pA/pF) was inhibited by ET-1. After [I.sub.Ca] stimulation by 1 [micro]M isoproterenol, ET-1 always inhibited the current by 32 [+ or -] 7% (P [is less than] 0.05), an effect that was suppressed by pretreating myocytes with pertussis toxin. Atrial natriuretic peptide (ANP) inhibited [I.sub.Ca] (41 [+ or -] 3%) by reducing intracellular cAMP concentration. In ANP-treated myocytes, the stimulatory effect of ET-1 on [I.sub.Ca] predominated (52 [+ or -] 7%). The inhibitory effect of ET-1 on [I.sub.Ca] was blocked by the [ET.sub.A] antagonist BQ-123, whereas the stimulatory effect was suppressed by the [ET.sub.B] agonist BQ-788. We conclude that ET-1 has opposite effects on [I.sub.Ca] depending on the baseline amplitude of current, and both subtype ET receptors are implicated in the signal transduction pathways. human cardiac cells; whole cell patch clamp

Boixel, Christophe, Sophie Tessier, Yves Pansard, Loic Lang-Lazdunski, Jean-Jacques Mercadier, and Stephane N. Hatem. Tyrosine kinase and protein kinase C regulate L-type [Ca.sup.2+] current cooperatively in human atrial myocytes. Am. J. Physiol. Heart Circ. Physiol. 278: H670-H676, 2000.--The effects of tyrosine protein kinases (TK) on the L-type [Ca.sup.2+] current ([I.sub.Ca]) were examined in whole cell patch-clamped human atrial myocytes. The TK inhibitors genistein (50 [micro]M), lavendustin A (50 [micro]M), and tyrphostin 23 (50 [micro]M) stimulated [I.sub.Ca] by 132 [+ or -] 18% (P [is less than] 0.001), 116 [+ or -] 18% (P [is less than] 0.05), and 60 [+ or -] 6% (P [is less than] 0.001), respectively. After [I.sub.Ca] stimulation by genistein, external application of isoproterenol (1 [micro]M) caused an additional increase in [I.sub.Ca]. Dialyzing the cells with a protein kinase A inhibitor suppressed the effect of isoproterenol on [I.sub.Ca] but not that of genistein. Inhibition of protein kinase C (PKC) by pretreatment of cells with 100 nM staurosporine or 100 nM calphostin C prevented the effects of genistein on [I.sub.Ca]. The PKC activator phorbol 12-myristate 13-acetate (PMA), after an initial stimulation (75 [+ or -] 17%, P 0.05), decreased [I.sub.Ca] (-36 [+ or -] 5%, P [is less than] 0.001). Once the inhibitory effect of PMA on [I.sub.Ca] had stabilized, genistein strongly stimulated the current (323 [+ or -] 25%, P [is less than] 0.05). Pretreating myocytes with genistein reduced the inhibitory effect of PMA on [I.sub.Ca]. We conclude that, in human atrial myocytes, TK inhibit [I.sub.Ca] via a mechanism that involves PKC. human cardiac cells; whole cell patch clamp; L-type calcium channels; tyrosine kinase inhibitors

Recent studies indicate that members of the multidrug-resistance protein (MRP) family belonging to ATP binding cassette type C (ABCC) membrane proteins extrude cyclic nucleotides from various cell types. This study aimed to determine whether MRP proteins regulate cardiac cAMP homeostasis. Here, we demonstrate that MRP4 is the predominant isoform present at the plasma membrane of cardiacmyocytes and that it mediates the efflux of cAMP in these cells. MRP4-deficient mice displayed enhanced cardiac myocyte cAMP formation, contractility, and cardiac hypertrophy at 9 mo of age, an effect that was compensated transiently by increased phosphodiesterase expression at young age. These findings suggest that cAMP extrusion via MRP4 acts together with phosphodiesterases to control cAMP levels in cardiac myocytes. [ABSTRACT FROM AUTHOR]

Investigates the role of the sodium/calcium ion exchange current (INa/Ca) in human atrial myocytes. Suppression of tail current; Recognition of action potential types; Effect of caffeine in internal calcium ion (Cai) transients; Mediation of beat-to-beat relationship between Cai and action potentials; Delayed afterdepolarizations among atrial myocytes.