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Ca2+ oscillations play an important role in various cell types. Thus, understanding the dynamical mechanisms underlying astrocytic Ca2+ oscillations is of great importance. The main purpose of this article was to investigate dynamical behaviors and bifurcation mechanisms associated with astrocytic Ca2+ oscillations, including stability of equilibrium and classification of different dynamical activities including regular and chaotic Ca2+ oscillations. Computation results show that part of the reason for the appearance and disappearance of spontaneous astrocytic Ca2+ oscillations is that they embody the subcritical Hopf and the supercritical Hopf bifurcation points. In more details, we theoretically analyze the stability of the equilibrium points and illustrate the regular and chaotic spontaneous calcium firing activities in the astrocytes model, which are qualitatively similar to actual biological experiment. Then, we investigate the effectiveness and the accuracy of our nonlinear dynamical mechanism analysis via computer simulations. These results suggest the important role of spontaneous Ca2+ oscillations in conjunction with the adjacent neuronal input that may help correlate the connection of both the glia and neuron.

Mitochondria match ATP supply to fluctuations in cellular energy requirements. Cellular energy requirements are often signaled to mitochondria by increases in the cytoplasmic concentration of Ca2+ ions. These increases in Ca2+ reach the mitochondrial matrix to regulate the proteins, enzymes and transporters required for mitochondrial ATP synthesis. Mitochondria may also limit energy demands by capturing the ion and shaping cytosolic Ca2+ signaling. Mitochondrial uptake of Ca2+ is driven by the substantial electrochemical gradient generated by the respiratory chain complexes. Although functional studies since the 1960s hinted at the nature of the Ca2+ channel involved, the molecular identity eluded physiologists until 2011 when the mitochondrial Ca2+ uniporter (MCU) gene was identified. MCU is a Ca2+-selective inwardly rectifying channel and a major pathway for the passage of Ca2+ ions from the cytoplasm into mitochondria. However, while well understood at the genetic and protein level, how MCU regulates cell function is unresolved. Understanding MCU regulation is of the utmost importance as disturbances in mitochondrial Ca2+ uptake accompanies several human diseases.

We studied the mechanisms by which carotid body glomus (type 1) cells produce spontaneous Ca2+oscillations in normoxia and hypoxia. In cells perfused with normoxic solution at 37°C, we observed relatively uniform, low-frequency Ca2+oscillations in >60% of cells, with each cell showing its own intrinsic frequency and amplitude. The mean frequency and amplitude of Ca2+oscillations were 0.6 ± 0.1 Hz and 180 ± 42 nM, respectively. The duration of each Ca2+oscillation ranged from 14 to 26 s (mean of ∼20 s). Inhibition of inositol (1,4,5)-trisphosphate receptor and store-operated Ca2+entry (SOCE) using 2-APB abolished Ca2+oscillations. Inhibition of endoplasmic reticulum Ca2+-ATPase (SERCA) using thapsigargin abolished Ca2+oscillations. ML-9, an inhibitor of STIM1 translocation, also strongly reduced Ca2+oscillations. Inhibitors of L- and T-type Ca2+channels (Cav; verapamil>nifedipine>TTA-P2) markedly reduced the frequency of Ca2+oscillations. Thus, Ca2+oscillations observed in normoxia were caused by cyclical Ca2+fluxes at the ER, which was supported by Ca2+influx via Ca2+channels. Hypoxia (2–5% O2) increased the frequency and amplitude of Ca2+oscillations, and Cavinhibitors (verapamil>nifedipine>>TTA-P2) reduced these effects of hypoxia. Our study shows that Ca2+oscillations represent the basic Ca2+signaling mechanism in normoxia and hypoxia in CB glomus cells.

Ca2+ oscillations and consequent Ca2+/calmodulin-dependent protein kinase II (CaMKII) activation are required for embryogenesis, as well as neuronal, immunological, and cardiac signaling. Fertilization directly results in Ca2+ oscillations, but the resultant pattern of CaMKII activity remains largely unclear. To address this gap, we first employed the one existing biosensor for CaMKII activation. This sensor, Camui, comprises CaMKIIα and therefore solely reports on the activation of this CaMKII variant. Additionally, to detect the activity of all endogenous CaMKII variants simultaneously, we constructed a substrate-based sensor for CaMKII activity, FRESCA ( FRE T-based s ensor for C aMKII a ctivity). To examine the differential responses of the Camui and FRESCA sensors, we used several approaches to stimulate Ca2+ release in mouse eggs, including addition of phospholipase Cζ cRNA, which mimics natural fertilization. We found that the Camui response is delayed or terminates earlier than the FRESCA response. FRESCA enables assessment of endogenous CaMKII activity in real-time by both fertilization and artificial reagents, such as Sr2+, which also leads to CaMKII activation. FRESCA's broad utility will be important for optimizing artificial CaMKII activation for clinical use to manage infertility. Moreover, FRESCA provides a new view on CaMKII activity, and its application in additional biological systems may reveal new signaling paradigms in eggs, as well as in neurons, cardiomyocytes, immune cells, and other CaMKII-expressing cells.

Sensitive sound detection within the mammalian cochlea is performed by hair cells surrounded by cochlear fluids. Maintenance of cochlear fluid homeostasis and tight regulation of intracellular conditions in hair cells are crucial for the auditory transduction process but can be impaired by intense sound stimulation. After a short, intense low-frequency sound, the cochlea shows the previously described “bounce phenomenon,” which manifests itself as slow oscillatory changes of hearing thresholds and otoacoustic emissions. In this study, distortion product otoacoustic emissions (DPOAEs) were recorded after Mongolian gerbils were exposed to intense low-frequency sounds (200 Hz, 100 dB SPL) with different exposure times up to 1 h. After all sound exposure durations, a certain percentage of recordings (up to 80% after 1.5-min-long exposure) showed oscillatory DPOAE changes, similar to the bounce phenomenon in humans. Changes were quite uniform with respect to size and time course, and they were independent from sound exposure duration. Changes showed states of hypo- and hyperactivity with either state preceding the other. The direction of changes was suggested to depend on the static position of the cochlear operating point. As assessed with DPOAEs, no indication for a permanent damage after several or long exposure times was detected. We propose that sensitivity changes occur due to alterations of the mechanoelectrical transduction process of outer hair cells. Those alterations could be induced by different challenged homeostatic processes with slow electromotility of outer hair cells being the most plausible source of the bounce phenomenon. NEW & NOTEWORTHY Low-frequency, high-intensity sound can cause slowly cycling activity changes in the mammalian cochlea. We examined the effect of low-frequency sound duration on the degree of these alterations. We found that cochlear changes showed a stereotypical biphasic pattern independent of sound exposure duration, but the probability that significant changes occurred decreased with increasing sound duration. Despite exposure durations of up to 1 h, no permanent or transient impairments of the cochlea were detected.

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels control human β-cell insulin secretion. Here, we examined if HCN channels impact glucagon-like-peptide 1 (GLP-1) receptor modulation of islet Ca2+ handling. We found that Liraglutide (100nM LIRA), a GLP-1 analog, increased mouse β-cell Ca2+ oscillation frequency and cAMP levels in high (11 mM) but not low glucose. Similarly, a subset of human β-cells (65%) show LIRA-induced elevations in Ca2+ oscillation frequency (by 70%, P Disclosure K. E. Zaborska: None. K. L. Jordan: None. P. Dadi: None. M. Dickerson: None. S. M. Graff: None. D. Jacobson: None.

At fertilization in mice and humans, the activation of the egg is caused by a series of repetitive Ca2+ oscillations which are initiated by phospholipase-C(zeta)ζ that generates inositol-1,4,5-trisphophate (InsP3). Ca2+ oscillations and egg activation can be triggered in mature mouse eggs by incubation in Sr2+ containing medium, but this does not appear to be effective in human eggs. Here, we have investigated the reason for this apparent difference using mouse eggs, and human eggs that failed to fertilize after IVF or ICSI. Mouse eggs incubated in Ca2+-free, Sr2+-containing medium immediately underwent Ca2+ oscillations but human eggs consistently failed to undergo Ca2+ oscillations in the same Sr2+ medium. We tested the InsP3-receptor (IP3R) sensitivity directly by photo-release of caged InsP3 and found that mouse eggs were about 10 times more sensitive to InsP3 than human eggs. There were no major differences in the Ca2+ store content between mouse and human eggs. However, we found that the ATP concentration was consistently higher in mouse compared to human eggs. When ATP levels were lowered in mouse eggs by incubation in pyruvate-free medium, Sr2+ failed to cause Ca2+ oscillations. When pyruvate was added back to these eggs, the ATP levels increased and Ca2+ oscillations were induced. This suggests that ATP modulates the ability of Sr2+ to stimulate IP3R-induced Ca2+ release in eggs. We suggest that human eggs may be unresponsive to Sr2+ medium because they have a lower level of cytosolic ATP.

Summary Ca2+ oscillations that depend on inositol-1,4,5-trisphosphate (IP3) have been ascribed to biphasic Ca2+ regulation of the IP3 receptor (IP3R) or feedback mechanisms controlling IP3 levels in different cell types. IP3 uncaging in hepatocytes elicits Ca2+ transients that are often localized at the subcellular level and increase in magnitude with stimulus strength. However, this does not reproduce the broad baseline-separated global Ca2+ oscillations elicited by vasopressin. Addition of hormone to cells activated by IP3 uncaging initiates a qualitative transition from high-frequency spatially disorganized Ca2+ transients, to low-frequency, oscillatory Ca2+ waves that propagate throughout the cell. A mathematical model with dual coupled oscillators that integrates Ca2+-induced Ca2+ release at the IP3R and mutual feedback mechanisms of cross-coupling between Ca2+ and IP3 reproduces this behavior. Thus, multiple Ca2+ oscillation modes can coexist in the same cell, and hormonal stimulation can switch from the simpler to the more complex to yield robust signaling., Graphical Abstract, Highlights • Ca2+ oscillations driven by IP3R (class 1) and PLC (class 2) occur in the same cell • IP3 uncaging elicits brief and often spatially localized class 1 Ca2+ oscillations • GPCRs elicit whole-cell Ca2+ oscillations and waves via a hybrid class 2 mechanism • Dual Ca2+ feedback on IP3R and PLC ensures a robust response to hormonal stimulation, Cell Biology; Specialized Functions of Cells; Mathematical Biosciences

Although the effect of ocean acidification on fertilization success of marine organisms is increasingly well documented, the underlying mechanisms are not completely understood. The fertilization success of broadcast spawning invertebrates depends on successful sperm-egg collisions, gamete fusion, and standard generation of Ca2+ oscillations. Therefore, the realistic effects of future ocean pCO2 levels on these specific aspects of fertilization of Tegillarca granosa were investigated in the present study through sperm velocity trials, fertilization kinetics model analysis, and intracellular Ca2+ assays, respectively. Results obtained indicated that ocean acidification significantly reduced the fertilization success of T. granosa, which could be accountable by (i) decreased sperm velocity hence reducing the probability for sperm-egg collisions; (ii) lowered probability of gamete fusion for each gamete collision event; and (iii) disrupted intracellular Ca2+ oscillations.

// Kunkun Xia 1, 2, * , Zegang Ma 3, 2, * , Jianxin Shen 4 , Menghan Li 4 , Baoke Hou 2 , Ming Gao 2 , Shuijun Zhang 1 and Jie Wu 1, 2, 3, 4 1 Department of Hepatobiliary and Pancreatic Surgery, First Affiliated Hospital of Zhengzhou University, Zhengzhou, China 2 Department of Neurobiology, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, AZ, USA 3 Department of Physiology, Shandong Provincial Key Laboratory of Pathogenesis and Prevention of Neurological Disorders, Shandong Provincial Collaborative Innovation Center for Neurodegenerative Disorders and State Key Disciplines, Physiology, Medical College of Qingdao University, Qingdao, China 4 Department of Physiology, Shantou University Medical College, Shantou, China * These authors have contributed equally to this work Correspondence to: Jie Wu, email: jie.wu@dignityhealth.org Keywords: 2-aminoethoxydiphenyl borate, store-operated Ca 2+ entry (SOCE), DPB161, Ca 2+ oscillations, rat submandibular cells Received: February 04, 2017 Accepted: May 06, 2017 Published: June 27, 2017 ABSTRACT Cellular Ca 2+ signals play a critical role in cell physiology and pathology. In most non-excitable cells, store-operated Ca 2+ entry (SOCE) is an important mechanism by which intracellular Ca 2+ signaling is regulated. However, few drugs can selectively modulate SOCE. 2-Aminoethoxydiphenyl borate (2APB) and its analogs (DPB162 and DPB163) have been reported to inhibit SOCE. Here, we examined the effects of another 2-APB analog, DPB161 on SOCE in acutely-isolated rat submandibular cells. Both patch-clamp recordings and Ca 2+ imaging showed that upon removal of extracellular Ca 2+ ([Ca 2+ ] o =0), rat submandibular cells were unable to maintain ACh-induced Ca 2+ oscillations, but restoration of [Ca 2+ ] o to refill Ca 2+ stores enable recovery of these Ca 2+ oscillations. However, addition of 50 μM DPB161 with [Ca 2+ ] o to extracellular solution prevented the refilling of Ca 2+ store. Fura-2 Ca 2+ imaging showed that DPB161 inhibited SOCE in a concentration-dependent manner. After depleting Ca 2+ stores by thapsigargin treatment, bath perfusion of 1 mM Ca 2+ induced [Ca 2+ ] i elevation in a manner that was prevented by DPB161. Collectively, these results show that the 2-APB analog DPB161 blocks SOCE in rat submandibular cells, suggesting that this compound can be developed as a pharmacological tool for the study of SOCE function and as a new therapeutic agent for treating SOCE-associated disorders.

The synergy between synaptic Glu release and astrocytic Glu-Na+ symport is essential to the signalling function of the tripartite synapse. Here we used kinetic data of astrocytic Glu transporters (EAAT) and the Na+/Ca2+ exchanger (NCX) to simulate Glu release, Glu uptake and subsequent Na+ and Ca2+ dynamics in the astrocytic leaflet microdomain following single release event. Model simulations show that Glu-Na+ symport differently affect intracellular [Na+] in synapses with different extent of astrocytic coverage. Surprisingly, NCX activity alone has been shown to generate markedly stable, spontaneous Ca2+ oscillation in the astrocytic leaflet. These on-going oscillations appear when NCX operates either in the forward or reverse direction. We conjecture that intrinsic NCX activity may play a prominent role in the generation of astrocytic Ca2+ oscillations.

Regulated mucin secretion from specialized goblet cells by exogenous agonist-dependent (stimulated) and -independent (baseline) manner is essential for the function of the epithelial lining. Over extended periods, baseline release of mucin can exceed quantities released by stimulated secretion, yet its regulation remains poorly characterized. We have discovered that ryanodine receptor-dependent intracellular Ca2+ oscillations effect the dissociation of the Ca2+-binding protein, KChIP3, encoded by KCNIP3 gene, from mature mucin-filled secretory granules, allowing for their exocytosis. Increased Ca2+ oscillations, or depleting KChIP3, lead to mucin hypersecretion in a human differentiated colonic cell line, an effect reproduced in the colon of Kcnip3-/- mice. Conversely, overexpressing KChIP3 or abrogating its Ca2+-sensing ability, increases KChIP3 association with granules, and inhibits baseline secretion. KChIP3 therefore emerges as the high-affinity Ca2+ sensor that negatively regulates baseline mucin secretion. We suggest KChIP3 marks mature, primed mucin granules, and functions as a Ca2+ oscillation-dependent brake to control baseline secretion. This work was funded by grants from the Spanish Ministry of Economy and Competitiveness (BFU2013-44188-P to VM, SAF2015-69762R to MAV and SAF2017-89554-R to JRN) and FEDER Funds. We acknowledge support of the Spanish Ministry of Economy and Competitiveness, through the Programmes “Centro de Excelencia Severo Ochoa 2013- 2017” (SEV-2012-0208 & SEV-2013-0347) and Maria de Maeztu Units of Excellence in R&D (MDM-2015- 0502). This work reflects only the authors’ views, and the EU Community is not liable for any use that may be made of the information contained therein.

Islet β-cells are responsible for secreting all circulating insulin in response to rising plasma glucose concentrations. These cells are a phenotypically diverse population that express great functional heterogeneity. In mice, certain β-cells (termed ‘hubs’) have been shown to be crucial for dictating the islet response to high glucose, with inhibition of these hub cells abolishing the coordinated Ca2+ oscillations necessary for driving insulin secretion. These β-cell hubs were found to be highly metabolic and susceptible to pro-inflammatory and glucolipotoxic insults. In this study, we explored the importance of hub cells in human by constructing mathematical models of Ca2+ activity in human islets. Our simulations revealed that hubs dictate the coordinated Ca2+ response in both mouse and human islets; silencing a small proportion of hubs abolished whole-islet Ca2+ activity. We also observed that if hubs are assumed to be preferentially gap junction coupled, then the simulations better adhere to the available experimental data. Our simulations of 16 size-matched mouse and human islet architectures revealed that there are species differences in the role of hubs; Ca2+ activity in human islets was more vulnerable to hub inhibition than mouse islets. These simulation results not only substantiate the existence of β-cell hubs, but also suggest that hubs may be favorably coupled in the electrical and metabolic network of the islet, and that targeted destruction of these cells would greatly impair human islet function.

Intracellular Ca2+ concentration ([Ca2+]i) disorder is one of the important pathogeneses of hypertension. Phillygenin (Phi) is a lignan compound found in medicinal plants and certain functional foods. In this paper, an event was first noticed that spontaneously hypertensive rats after treatment with 2.5–10 mg/kg Phi exhibited a significant reduction in systolic and diastolic pressure. In addition, it was also verified that Phi has a significant inhibitory effect on inositol 1,4,5-trisphosphate receptors-mediated Ca2+ release from calcium stores in H9C2 cells. To evaluate the antihypertensive properties of Phi and explore its antihypertension mechanism, an alkynyl modified Phi molecular probes were synthesized. Then, the protein PLCβ3 was captured and identified as a target of Phi on PLCβ3-dependent Ca2+ oscillation by a series of chemical biology strategy. And the evidence may be provide a good guidance of Phi containing functional food in dietary nutrition regulation for the prevention of hypertension.

Pancreatic islets can adapt to oscillatory glucose to produce synchronous insulin pulses. Can islets adapt to other oscillatory stimuli, specifically insulin? To answer this question, we stimulated islets with pulses of exogenous insulin and measured their Ca2+ oscillations. We observed that sufficiently high insulin (> 500 nM) with an optimal pulse period (~ 4 min) could make islets to produce synchronous Ca2+ oscillations. Glucose and insulin, which are key stimulatory factors of islets, modulate islet Ca2+ oscillations differently. Glucose increases the active-to-silent ratio of phases, whereas insulin increases the period of the oscillation. To examine the dual modulation, we adopted a phase oscillator model that incorporated the phase and frequency modulations. This mathematical model showed that out-of-phase oscillations of glucose and insulin were more effective at synchronizing islet Ca2+ oscillations than in-phase stimuli. This finding suggests that a phase shift in glucose and insulin oscillations can enhance inter-islet synchronization.

On mammalian fertilization, long-lasting Ca2+ oscillations are induced in the egg by the fusing spermatozoon. While each transient Ca2+ increase in Ca2+ concentration ([Ca2+]) in the cytosol is due to Ca2+ release from the endoplasmic reticulum (ER), Ca2+ influx from outside is required for Ca2+ oscillations to persist. In this study, we investigated how Ca2+ influx is interrelated to the cycle of Ca2+ release and uptake by the intracellular Ca2+ stores during Ca2+ oscillations in fertilized mouse eggs. In addition to monitoring cytosolic [Ca2+] with fura-2, the influx rate was evaluated using Mn2+ quenching technique, and the change in [Ca2+] in the ER lumen was visualized with a targeted fluorescent probe. We found that the influx was stimulated after each transient Ca2+ release and then diminished gradually to the basal level, and demonstrated that the ER Ca2+ stores once depleted by Ca2+ release were gradually refilled until the next Ca2+ transient to be initiated. Experiments altering extracellular [Ca2+] in the middle of Ca2+ oscillations revealed the dependence of both the refilling rate and the oscillation frequency on the rate of Ca2+ influx, indicating the crucial role of Ca2+ influx in determining the intervals of Ca2+ transients. As for the influx pathway supporting Ca2+ oscillations to persist, STIM1/Orai1-mediated store-operated Ca2+ entry (SOCE) may not significantly contribute, since neither known SOCE blockers nor the expression of protein fragments that interfere the interaction between STIM1 and Orai1 inhibited the oscillation frequency or the influx rate.

[Ca(2+)](i) oscillations are irregular and heterogeneous.The correlations between NFκB/STAT3-GFP transcription and [Ca(2+)](i) spike amplitude/cumulative spike duration are revealed by simultaneous monitoring in single cells and validated in cell population.[Ca(2+)](i) oscillations regulate transcription through [Ca(2+)](i) spike amplitude and cumulative spike duration.How irregular [Ca(2+)](i) oscillations control transcription is crucial for understanding biological [Ca(2+)](i) signal-regulated events. Agonist-stimulated [Ca(2+)](i) oscillations are universally irregular in their kinetics. How irregular [Ca(2+)](i) oscillations dynamically regulate agonist-stimulated downstream events has not been studied. To overcome the obstacles of irregularity and heterogeneity of [Ca(2+)](i) oscillations, agonist-stimulated [Ca(2+)](i) signaling and NFκB/STAT3-GFP nuclear translocation were simultaneously monitored in each single cell examined. The cause-effect relationship between [Ca(2+)](i) oscillation parameters and transcriptional activities was validated in cell populations through irregular [Ca(2+)](i) oscillations with varied parameters. The time duration of cumulative [Ca(2+)](i) elevations reaching the threshold [Ca(2+)](i) level for a transcriptional factor activation and [Ca(2+)](i) spike amplitude was found to control agonist-stimulated transcription and gene expression.

In many cell types, intracellular calcium is released from internal stores through calcium release channels which are distributed in clusters with a few tens of channels. Localized calcium release events, i.e. Ca 2 + puffs, are subjected to stochastic channel dynamics and fluctuations of environmental calcium. Driven by the internal channel noise or external calcium noise, the localized calcium puffs show a coherence resonance phenomenon at weak stimulus. Our study indicates that coherent calcium puffs with an enhanced periodicity can be achieved with external calcium noise more easily than with internal channel noise.

Ryanodine receptor (RyR)-mediated Ca(2+) dysregulation is associated with Alzheimer's disease (AD) neuropathology. Using 2-photon Ca(2+) imaging and patch clamp recordings in brain slice preparations from young 3xTg-AD and NonTg control mice, we recently demonstrated that RyR-mediated Ca(2+) -induced Ca(2+) release (CICR) is substantially increased within dendrites from AD neurons, such that synaptic stimulation alone is sufficient to generate aberrant CICR. We also observed supra-additive Ca(2+) release upon coincident RyR activation with synaptic stimulation in 3xTg-AD mice. Here, we describe an additional observed phenomenon: generation of patterned Ca(2+) oscillations in the spines and dendrites from AD neurons upon coincident RyR and synaptic stimulation. As the temporal entrainment of Ca(2+) signals influences many downstream cellular and synaptic functions, these abnormal oscillatory patterns may be associated with the structural and functional breakdown of synapses in AD.

We have studied the effect of a particular kind of non-Gaussian noise (NGN), mainly of its deviation q from Gaussian noise, on the intercellular calcium (Ca2+) oscillations in an array of bidirectionally coupled cells. It is found that as q is increased, the Ca2+ oscillation becomes the most regular at an intermediate optimal q value, representing the occurrence of coherence resonance (CR). This deviation-induced CR behavior shows that the intercellular Ca2+ oscillations of the coupled cells can be enhanced and even optimized by the appropriate NGN. This result provides a new insight into the constructive role of the NGN on the transmission of Ca2+ signaling in coupled cells.

Glial cells, especially astrocytes, are not merely supportive cells, but are important partners to neighboring cells, including neurons, vascular cells, and other glial cells. Although glial cells are not excitable in terms of electrophysiology, they have been shown to generate synchronized Ca(2+) transients (Ca(2+) oscillations) through mechanisms of chemical coupling. Until recently, Ca(2+) transients in astrocytes were thought to be totally dependent on neuronal activities, because astrocytes express a large variety of receptors for neurotransmitters and surround almost all synapses at which neurotransmitters are spilled over to stimulate astrocytes. In addition, however, astrocytes have been shown to release diffusible substances, so-called 'gliotransmitters', and Ca(2+) transients in astrocytes are therefore also triggered by astrocytic activities, leading to propagation of Ca(2+) transients or Ca(2+) waves. In these processes, the gliotransmitter ATP and activation of P2Y receptors play central roles. Interestingly, astrocytes evoke Ca(2+) transients when neurons are not present, suggesting that astrocytes themselves can initiate and control Ca(2+) transients. Astrocytic Ca(2+) transients are observed even in vivo, through mechanisms of chemical coupling by gliotransmitters, but they are less frequent and synchronous than those in vitro. Although we have not yet clarified their significance in the central nervous system, astrocytic Ca(2+) transients are dramatically affected by pathological conditions, suggesting that, in addition to physiological events, they might be closely involved in disorders in the central nervous system.

Ginsenoside Rg1, the main active ingredient of Ginseng Radix which is a famous Chinese medicine, is widely used as an anti-stress, anti-aging and neurological performance improving agent. In this study, we used calcium imaging and whole-cell patch clamp techniques to investigate the effect of Ginsenoside Rg1 on spontaneous and synchronous Ca 2+ oscillations and the possible mechanisms in primarily cultured hippocampal neuronal networks. We found that Ginse- noside Rg1 could decrease the frequencies of spontaneous and synchronous Ca 2+ oscillations and inhibit the amplitude of high-voltage activated calcium channel currents. These results provided the experimental evidence for the clinical applica- tion of Rg1 as a neuroprotector on the cellular level, and enriched the theoretical system of Chinese medicine.

A mathematical model proposed by Grubelnk et al. [Biophys. Chew,. 94 (2001) 59] is employed to study the physiological role of mitochondria and the cytosolic proteins in generating complex Ca2+ oscillations. Intracel-lular bursting calcium oscillations of point–point, point–cycle and two-folded limit cycle types are observed and explanations are given based on the fast/slow dynamical analysis, especially for point–cycle and two-folded limit cycle types, which have not been reported before. Furthermore, synchronization of coupled bursters of Ca2+ oscillations via gap junctions and the effect of bursting types on synchronization of coupled cells are studied. It is argued that bursting oscillations of point–point type may be superior to achieve synchronization than that of point–cycle type.

A physiological membrane-receptor agonist typically stimulates oscillations, of varying frequencies, in cytosolic Ca2+ concentration ([Ca2+]i). Whether and how [Ca2+]i oscillation frequency regulates agonist-stimulated downstream events, such as gene expression, in non-excitable cells remain unknown. By precisely manipulating [Ca2+]i oscillation frequency in histamine-stimulated vascular endothelial cells (ECs), we demonstrate that the gene expression of vascular cell adhesion molecule 1 (VCAM1) critically depends on [Ca2+]i oscillation frequency in the presence, as well as the absence, of histamine stimulation. However, histamine stimulation enhanced the efficiency of [Ca2+]i-oscillation-frequency-regulated VCAM1 gene expression, versus [Ca2+]i oscillations alone in the absence of histamine stimulation. Furthermore, a [Ca2+]i oscillation frequency previously observed to be the mean frequency in histamine-stimulated ECs was found to optimize VCAM1 mRNA expression. All the above effects were abolished or attenuated by blocking histamine-stimulated generation of intracellular reactive oxygen species (ROS), another intracellular signaling pathway, and were restored by supplementary application of a low level of H2O2. Endogenous NF-κB activity is similarly regulated by [Ca2+]i oscillation frequency, as well as its co-operation with ROS during histamine stimulation. This study shows that [Ca2+]i oscillation frequency cooperates with ROS to efficiently regulate agonist-stimulated gene expression, and provides a novel and general strategy for studying [Ca2+]i signal kinetics in agonist-stimulated downstream events.

Magnesium ions (Mg(2+)) play a fundamental role in cellular function, but the cellular dynamic changes of intracellular Mg(2+) remain poorly delineated. The present study aims to clarify whether the concentration of intracellular Mg(2+) possibly changes cyclically in association with rhythmic contraction and intracellular Ca(2+) oscillation in cultured cardiac myocytes from neonatal rats. To do this, we performed a noise analysis of fluctuations in the concentration of intracellular Mg(2+) in cardiac myocytes. The concentration was estimated by loading cells with either Mg-fluo4/AM or KMG-20/AM. Results revealed that the intensity of Mg-fluo-4 or KMG-20 fluorescence fluctuated cyclically in association with the rhythmic contraction of cardiac myocytes. In addition, the simultaneous measurement of Fura2 and Mg-fluo-4 fluorescence revealed phase differences between the dynamics of the two signals, suggesting that the cyclic changes in the Mg-fluo-4 or KMG-20 fluorescent intensity actually reflected the changes in intracellular Mg(2+). The complete termination of spontaneous rhythmic contractions did not abolish Mg(2+) oscillations, suggesting that the rhythmic fluctuations in intracellular Mg(2+) did not result from mechanical movements. We suggest that the concentration of intracellular Mg(2+) changes cyclically in association with spontaneous, cyclic changes in the concentration of intracellular Ca(2+) of cardiac myocytes. A noise analysis of the fluctuation of subtle changes in fluorescence intensity could contribute to the elucidation of novel functional roles of Mg(2+) in cells.

Isolated and cultured neonatal cardiac myocytes contract spontaneously and cyclically. The contraction rhythms of two isolated cardiac myocytes, each of which beats at different frequencies at first, become synchronized after the establishment of mutual contacts, suggesting that mutual entrainment occurs due to electrical and/or mechanical interactions between two myocytes. The intracellular concentration of free Ca(2+) also changes rhythmically in association with the rhythmic contraction of myocytes (Ca(2+) oscillation), and such a Ca(2+) oscillation was also synchronized among cultured cardiac myocytes. In this study, we investigated whether intercellular communication other than via gap junctions was involved in the intercellular synchronization of intracellular Ca(2+) oscillation in spontaneously beating cultured cardiac myocytes. Treatment with either blockers of gap junction channels or an un-coupler of E-C coupling did not affect the intercellular synchronization of Ca(2+) oscillation. In contrast, treatment with a blocker of P2 purinoceptors resulted in the asynchronization of Ca(2+) oscillatory rhythms among cardiac myocytes. The present study suggested that the extracellular ATP-purinoceptor system was responsible for the intercellular synchronization of Ca(2+) oscillation among cardiac myocytes.

The effects of beta amyloid (Abeta) on cytoplasmic Ca(2+) ([Ca(2+)](c)) have been studied extensively, but the current literature on this aspect is confusing. We reported that 20 microM Abeta(25-35) significantly inhibited the synchronized spontaneous cytoplasmic Ca(2+) transients immediately after application, whereas it had little effect on the baseline [Ca(2+)](c) concentration in neurons. Abeta(1-42) had a similar effect on the Ca(2+) transients as Abeta(25-35), while it increased baseline [Ca(2+)](c) concentration gradually. However, Abeta(1-40) had little effect on either Ca(2+) transients or baseline [Ca(2+)](c). Such differential effects of Abeta on Ca(2+) signals might explain, at least partially, the confusing observations from the previous studies and provide important therapeutic implications for preventing or reversing early neuron damage in Alzheimer's disease.

Calcium oscillations regulate several cellular processes by activating particular proteins. Most theoretical studies focused on the idealized situation of infinitely long oscillations. Here we analyze information transfer by time-limited calcium spike trains. We show that proteins can be selectively activated in a resonance-like manner by time-limited spike trains of different frequencies, while infinitely long oscillations do not show this resonance phenomenon. We found that proteins are activated more specifically by shorter oscillatory signals with narrower spikes.

Astrocyte have glutamate (Glu) receptors as well as neurons do and they have been suggested to participate in the information processing of brain with neurons. The cultured hippocampal astrocytes have spontaneous oscillation of intracellular Ca2+ concentration ([Ca2+]i). The application of Glu induces not only [Ca2+]i oscillation but also Ca2+ wave which is propagating among the astrocytes. In the present study, we proposed the PLCδ model which could induce some types of glutamate-induced [Ca2+]i responses and the intercellular Ca2+ wave observed in the experiment. Our simulation results suggested that PLCδ is a key molecule for [Ca2+]i oscillation and wave.

A mathematical model for bursting Ca 2+ oscillations is analysed from a physical point of view as a system of internally coupled fast and slow oscillators. We show that the fast subsystem determines the interburst frequency, whereas altering the kinetics of the slow processes changes the duration of the bursting phase in a resonant manner. The resonance effect appears between two oscillatory Ca 2+ -buffering mechanisms. This may be biologically important for a highly selective Ca 2+ signal transduction from cell receptors to target proteins.

Considering four coupled identical and non-identical bursters with different topological types, both of the different synchronization transition paths and influence of the oscillatory patterns on synchronization are studied. Our results reveal that the phenomena of multi-time scale, phase-locking, chaos and anti-phase synchronization transitions can be separately found in the coupled systems by varying the coupling strength. The above analysis of synchronization transition could provide us with a further clue for better understanding the mechanism of intracellular Ca2+ signaling.

Our group has studied the origin of Ca2+ oscillations triggered by the cardiotonic steroid ouabain, a highly specific ligand of Na+-K+-ATPase. It has been shown that these low frequency oscillation...

We present a new model for inositol triphosphate (IP3)-induced cytosolic Ca2+ oscillations in non-excitable cells. The model includes the various Ca2+ in- and efflux pathways reported to exist in these cells. In particular, it features the complex regulation of the Ca2+ release from the endoplasmic reticulum (ER) by IP3, cytosolic Ca2+ and Ca2+ in the ER. Bifurcation analysis revealed that the model accurately predicts the cytosolic Ca2+ dynamics in a typical non-excitable cell. Diffusional coupling of this model in a two-dimensional network shows hysteresis and bistability in its collective dynamics. Depending on the strength of the diffusion constant, we find traveling or spiral waves as solutions of this system.

We investigate the various types of complex Ca2+ oscillations which can arise in a model based on the mechanism of Ca2+-induced Ca2+ release (CICR), that takes into account the Ca2+-stimulated degradation of inositol 1,4,5-trisphosphate (InsP3) by a 3-kinase. This model was previously proposed in the course of an investigation of plausible mechanisms capable of generating complex Ca2+ oscillations (Borghans et al., 1997). Besides simple periodic behavior, this model for cytosolic Ca2+ oscillations in nonexcitable cells shows complex oscillatory phenomena like bursting or chaos. We show that the model also admits a coexistence between two stable regimes of sustained oscillations (birhythmicity). The occurrence of these various modes of oscillatory behavior is analysed by means of bifurcation diagrams. Complex oscillations are characterized by means of Poincare sections, power spectra and Lyapounov exponents. The results point to the role of self-modulation of the InsP3 signal by 3-kinase as a possible source for complex temporal patterns in Ca2+ signaling.

Recent evidence underlines a key role of mitochondrial Ca2+ fluxes in cell Ca2+ signalling. We present here a kinetic model simulating the Ca2+ fluxes generated by mitochondria during mitochondrial Ca(2+)-induced Ca2+ release (mCICR) resulting from the operation of the permeability transition pore (PTP). Our model connects the Ca2+ fluxes through the ruthenium redsensitive Ca2+ uniporter, the respiration-dependent and passive H+ fluxes, the rate of oxygen consumption, the movements of weak acids across the mitochondrial membrane, the electrical transmembrane potential (delta psi), and operation of the PTP. We find that two factors are crucial to account for the various mCICR profiles that can be observed experimentally: (i) the dependence of PTP opening and closure on matrix pH (pHi), and (ii) the relative inhibition of the respiratory rate consecutive to PTP opening. The resulting model can simulate irreversible Ca2+ efflux from mitochondria, as well as the genesis of damped or sustained Ca2+ oscillations, and of single Ca2+ spikes. The model also simulates the main features of mCICR, i.e. the threshold-dependence of mCICR triggering, and the all-or-nothing nature of mCICR operation. Our model should appear useful to further mathematically address the consequences of mCICR on the spatiotemporal organisation of Ca2+ signals, as a 'plug-in' module for the existing models of cell Ca2+ signalling.

Changes in the intracellular concentration of free calcium ([Ca2+]i) regulate diverse cellular processes including fertilization. In mammalian eggs, the [Ca2+]i changes induced by the sperm unfold in a pattern of periodical rises, also known as [Ca2+]i oscillations. The source of Ca2+ during oscillations is the endoplasmic reticulum ([Ca2+]ER), but it is presently unknown how [Ca2+]ER is regulated. Here, we show using mouse eggs that [Ca2+]i oscillations induced by a variety of agonists, including PLCζ, SrCl2 and thimerosal, provoke simultaneous but opposite changes in [Ca2+]ER and cause differential effects on the refilling and overall load of [Ca2+]ER. We also found that Ca2+ influx is required to refill [Ca2+]ER, because the loss of [Ca2+]ER was accelerated in medium devoid of Ca2+. Pharmacological inactivation of the function of the mitochondria and of the Ca2+-ATPase pumps PMCA and SERCA altered the pattern of oscillations and abruptly reduced [Ca2+]ER, especially after inactivation of mitochondria and SERCA functions. We also examined the expression of SERCA2b protein and found that it was expressed throughout oocyte maturation and attained a conspicuous cortical cluster organization in mature eggs. We show that its overexpression reduces the duration of inositol-1,4,5-trisphosphate-induced [Ca2+]i rises, promotes initiation of oscillations and enhances refilling of [Ca2+]ER. Collectively, our results provide novel insights on the regulation of [Ca2+]ER oscillations, which underlie the unique Ca2+-signalling system that activates the developmental program in mammalian eggs. ispartof: Journal of Cell Science vol:126 issue:24 pages:5714-5724 ispartof: location:England status: published

Current models for the agonist-induced activation of Ca2+ entry from the extracellular medium in non-excitable cells generally emphasize a capacitative mechanism whereby Ca2+ entry is activated simply as a result of the emptying of intracellular Ca2+ stores, without any direct involvement of inositol phosphates. To date, the activation and control of Ca2+ entry have generally been studied under conditions where the agonist-sensitive stores undergo a profound and sustained depletion. However, responses under more normal physiological conditions typically involve the cyclical release and refilling of the stores associated with oscillations in [Ca2+], and the nature and control of entry under these conditions has received relatively little attention. In this study, using isolated cells from the exocrine avian nasal gland as a model system, we show that: (a) the agonist-enhanced rate of Mn2+ quench is independent of the cyclical emptying and refilling of the agonist-sensitive Ca2+ pool during oscillations; (b) the Ca2+ entry pathway is maintained in an activated state for extended periods following inhibition of oscillations under conditions in which agonist-sensitive stores can be shown to be full; (c) no Ca2+ entry could be detected in oscillating cells in experiments that followed a definitive protocol for the demonstration of capacitative entry; and (d) on initial exposure to low agonist concentrations, activation of Ca2+ entry preceded any detectable release of Ca2+ from the stores. We conclude that the essential characteristics of the control of Ca2+ entry during oscillations are incompatible with current capacitative models.

This study was undertaken to localize ryanodine-sensitive Ca2+ stores in human oocytes and to evaluate their role in the Ca2+ oscillations responsible for oocyte activation at fertilization. The addition of ryanodine provoked a Ca2+ discharge from stores localized throughout the ooplasm with the exception of the cortical and subcortical peripheral regions. The ryanodine-induced discharge was typically followed by a short series of Ca2+ oscillations that only involved the cytoplasmic region populated by the ryanodine-sensitive stores. In contrast, the Ca2+ oscillations induced by the thiol reagent thimerosal or by spermatozoa at fertilization were of a much longer duration and also involved ryanodine-insensitive stores. Presumably, these ryanodine-insensitive stores are sensitive to inositol 1,4,5-trisphosphate (InsP3). The addition of ryanodine to oocytes during ongoing thimerosal- or sperm-induced Ca2+ oscillations inhibited the oscillations. These data suggest a co-operation between the ryanodine-sensitive and ryanodine-insensitive stores in maintaining the sperm-induced Ca2+ oscillations. In this two-store oscillation model, each periodic [Ca2+]i increase is triggered by a Ca2+ discharge from the peripheral, InsP3-sensitive stores inducing Ca(2+)-induced Ca2+ release from the ryanodine-sensitive stores. However, the pacemaker frequency of the Ca2+ discharges from the InsP3-sensitive stores is conditioned by the actual physiological state of the ryanodine-sensitive stores.

A new model for intracellular Ca2+ oscillations is presented. The new model reinterprets two previous models, the ICC and CICR mechanisms, and incorporates the bell-shaped dependence of Ca2+ release on cytosolic [Ca2+]. Complex oscillations and chaos are found with this new model, confirming experimental observations of complex oscillations. A rich bifurcation sequence is found for the model as the stimulation due to agonist (R) is varied, including a period doubling route to chaos and a period-adding sequence of mixed-mode states.