scholarly journals Murine Electrophysiological Models of Cardiac Arrhythmogenesis

2017 ◽  
Vol 97 (1) ◽  
pp. 283-409 ◽  
Author(s):  
Christopher L.-H. Huang
Keyword(s):  
Structural Change ◽  
Surface Membrane ◽  
Experimental Studies ◽  
Cardiac Activity ◽  
Cardiac Pacing ◽  
Ventricular Myocardium ◽  
Cellular Tissue ◽  
Cardiac Arrhythmogenesis ◽  
Voltage Dependent ◽  
Intracellular Ca

Cardiac arrhythmias can follow disruption of the normal cellular electrophysiological processes underlying excitable activity and their tissue propagation as coherent wavefronts from the primary sinoatrial node pacemaker, through the atria, conducting structures and ventricular myocardium. These physiological events are driven by interacting, voltage-dependent, processes of activation, inactivation, and recovery in the ion channels present in cardiomyocyte membranes. Generation and conduction of these events are further modulated by intracellular Ca2+ homeostasis, and metabolic and structural change. This review describes experimental studies on murine models for known clinical arrhythmic conditions in which these mechanisms were modified by genetic, physiological, or pharmacological manipulation. These exemplars yielded molecular, physiological, and structural phenotypes often directly translatable to their corresponding clinical conditions, which could be investigated at the molecular, cellular, tissue, organ, and whole animal levels. Arrhythmogenesis could be explored during normal pacing activity, regular stimulation, following imposed extra-stimuli, or during progressively incremented steady pacing frequencies. Arrhythmic substrate was identified with temporal and spatial functional heterogeneities predisposing to reentrant excitation phenomena. These could arise from abnormalities in cardiac pacing function, tissue electrical connectivity, and cellular excitation and recovery. Triggering events during or following recovery from action potential excitation could thereby lead to sustained arrhythmia. These surface membrane processes were modified by alterations in cellular Ca2+ homeostasis and energetics, as well as cellular and tissue structural change. Study of murine systems thus offers major insights into both our understanding of normal cardiac activity and its propagation, and their relationship to mechanisms generating clinical arrhythmias.

Role of the Cilia Membrane in Control of Microtubule Sliding

1980 ◽  
Vol 38 ◽  
pp. 612-615
Author(s):  
Edna S. Kaneshiro
Keyword(s):  
Control Mechanism ◽  
Beat Frequency ◽  
Surface Membrane ◽  
Ciliary Membrane ◽  
Ciliary Beating ◽  
Ciliary Reversal ◽  
Voltage Dependent ◽  
Reversal Mechanism ◽  
And Function

It is currently believed that ciliary beating results from microtubule sliding which is restricted in regions to cause bending. Cilia beat can be modified to bring about changes in beat frequency, cessation of beat and reversal in beat direction. In ciliated protozoans these modifications which determine swimming behavior have been shown to be related to intracellular (intraciliary) Ca2+ concentrations. The Ca2+ levels are in turn governed by the surface ciliary membrane which exhibits increased Ca2+ conductance (permeability) in response to depolarization. Mutants with altered behaviors have been isolated. Pawn mutants fail to exhibit reversal of the effective stroke of ciliary beat and therefore cannot swim backward. They lack the increased inward Ca2+ current in response to depolarizing stimuli. Both normal and pawn Paramecium made leaky to Ca2+ by Triton extrac¬tion of the surface membrane exhibit backward swimming only in reactivating solutions containing greater than IO-6 M Ca2+ Thus in pawns the ciliary reversal mechanism itself is left operational and only the control mechanism at the membrane is affected. The topographic location of voltage-dependent Ca2+ channels has been identified as a component of the ciliary mem¬brane since the inward Ca2+ conductance response is eliminated by deciliation and the return of the response occurs during cilia regeneration. Since the ciliary membrane has been impli¬cated in the control of Ca2+ levels in the cilium and therefore is the site of at least one kind of control of microtubule sliding, we have focused our attention on understanding the structure and function of the membrane.

Stimulation of 5-HT2 Receptors in Prefrontal Pyramidal Neurons Inhibits Cav1.2 L-Type Ca2+Currents Via a PLCβ/IP3/Calcineurin Signaling Cascade

2002 ◽  
Vol 87 (5) ◽  
pp. 2490-2504 ◽  
Author(s):  
Michelle Day ◽  
Patricia A. Olson ◽  
Josef Platzer ◽  
Joerg Striessnig ◽  
D. James Surmeier
Keyword(s):  
Pyramidal Neurons ◽  
Inositol Trisphosphate ◽  
Cell Voltage ◽  
Signaling Cascade ◽  
Channel Modulation ◽  
Receptor Modulation ◽  
Bath Application ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
Layer V

There is growing evidence linking alterations in serotonergic signaling in the prefrontal cortex to the etiology of schizophrenia. Prefrontal pyramidal neurons are richly innervated by serotonergic fibers and express high levels of serotonergic 5-HT2-class receptors. It is unclear, however, how activation of these receptors modulates cellular activity. To help fill this gap, whole cell voltage-clamp and single-cell RT-PCR studies of acutely isolated layer V–VI prefrontal pyramidal neurons were undertaken. The vast majority (>80%) of these neurons had detectable levels of 5-HT2A or 5-HT2C receptor mRNA. Bath application of 5-HT2 agonists inhibited voltage-dependent Ca2+ channel currents. L-type Ca2+ channels were a particularly prominent target of this signaling pathway. The L-type channel modulation was blocked by disruption of Gαq signaling or by inhibition of phospholipase Cβ. Antagonism of intracellular inositol trisphosphate signaling, chelation of intracellular Ca2+, or depletion of intracellular Ca2+ stores also blocked this modulation. Inhibition of the Ca2+-dependent phosphatase calcineurin prevented receptor-mediated modulation of L-type currents. Last, the 5-HT2 receptor modulation was robustly expressed in neurons from Cav1.3 knockout mice. These findings argue that 5-HT2receptors couple through Gαq proteins to trigger a phospholipase Cβ/inositol trisphosphate signaling cascade resulting in the mobilization of intracellular Ca2+, activation of calcineurin, and inhibition of Cav1.2 L-type Ca2+currents. This modulation and its blockade by atypical neuroleptics could have wide-ranging effects on synaptic integration and long-term gene expression in deep-layer prefrontal pyramidal neurons.

scholarly journals Cross-talk between Native Plasmalemmal Na+/Ca2+Exchanger and Inositol 1,4,5-Trisphosphate-sensitive Ca2+Internal Store inXenopusOocytes

2004 ◽  
Vol 279 (50) ◽  
pp. 52414-52424 ◽  
Author(s):  
Luisa M. Solís-Garrido ◽  
Antonio J. Pintado ◽  
Eva Andrés-Mateos ◽  
María Figueroa ◽  
Carlos Matute ◽  
...  
Keyword(s):  
Confocal Microscopy ◽  
Surface Membrane ◽  
Rabbit Serum ◽  
Caged Compounds ◽  
Reverse Transcription Pcr ◽  
Inositol 1,4,5 Trisphosphate ◽  
Intracellular Ca ◽  
Functional Consequences ◽  
Extracellular Sodium ◽  
Cortical Endoplasmic Reticulum

Because the presence of a native plasmalemmal Na+/Ca2+exchange (NCX) activity inXenopus laevisoocytes remains controversial, its possible functional role in these cells is poorly understood. Here, in experiments on control oocytes and oocytes overexpressing a cloned NCX1 cardiac protein, confocal microscopy combined with electrophysiological techniques reveal that these cells express an endogenous NCX protein forming a functional microdomain with inositol 1,4,5-trisphosphate receptors (InsP3R) that controls intracellular Ca2+in a restricted subplasmalemmal space. The following data obtained in control denuded oocytes are consistent with this view: (i) reverse transcription-PCR revealed that the oocyte expresses two transcripts for the NCX1 and NCX3 isoforms; (ii) immunofluorescence experiments showed that native NCX1 and InsP3Rs are largely codistributed in discrete areas of the plasma membrane in close apposition to the cortical endoplasmic reticulum shell; (iii) when stimulated by rabbit serum, which elevates intracellular Ca2+mediated by InsP3, voltage-clamped oocytes display a large and transient inward Ca2+-activated chloride current, ICl(Ca), as a result of the Ca2+rise at the inner surface membrane; (iv) this current is significantly enhanced by KB-R7943 and by an extracellular sodium-depleted medium, two maneuvers that prevent “Ca2+extrusion” via NCX; and (v) blocking NCX enhanced the ICl(Ca)elicited by InsP3but not by Ca2+photolysis in oocytes injected with the respective caged compounds. Moreover, overexpression of cardiac NCX1, confirmed by confocal microscopy, has functional consequences for the “Ca2+influx” but not for the serum-elicited “Ca2+efflux” mode of basal exchange activity and does not alter the number of endogenous NCX/InsP3Rs colocalization sites. Our results suggest that native NCX, because of its strategic position, may regulate InsP3-mediated Ca2+signaling during the early phases of oocyte maturation and/or fertilization, and furthermore foreign cardiac protein is excluded from the Ca2+microdomains surrounding the native NCX/InsP3Rs complex in the oocyte.

Abstract 261: Human IPS-Derived Cardiac Myocytes (hiPSC-CMs): How Good Are They as a Model for Cardiac Pacing and E-C Coupling?

2013 ◽  
Vol 113 (suppl_1) ◽  
Author(s):  
Martin Morad ◽  
Xiao-Hua Zhang ◽  
Hua Wei ◽  
Lars Cleemann
Keyword(s):  
Pluripotent Stem Cells ◽  
Voltage Dependence ◽  
Cardiac Pacing ◽  
Neonatal Rat ◽  
Ec Coupling ◽  
Adult Cardiomyocytes ◽  
Voltage Dependent ◽  
Rat Myocytes ◽  
Induced Pluripotent ◽  
Synthase Inhibitor

Derivation of cardiomyocytes from human induced pluripotent stem cells has opened a new field of biology where hiPSC-CM are being used as electrophysiological models of human cardiovascular physiology and pathology. Whether hiPS-CM represent also reliable Ca 2+ signaling and pacemaking models for the mammalian myocytes remains to be determined. Here we evaluate the EC-coupling and spontaneous pacemaking properties of human iPS-CM in detail and compare them to those of native mammalian myocytes. iPS-CMs, dissociated after ~40 days of differentiation and voltage-clamped at -50 mV, showed spontaneous beating and Ca 2+ oscillations that activated in-phase I NCX oscillations at holding potentials between -60 and +20mV, while I f activated negative to -75mV. Withdrawal of [Ca 2+ ] o and application of NCX-blocker (KBR- 7943) or tetracaine rapidly and reversibly inhibited spontaneous Ca 2+ -oscillations. Nifedipine and NO-synthase inhibitor L-NAME failed to alter spontaneous beating. Identical sets of data as these were also obtained from neonatal rat myocytes (NRM), suggesting that SR Ca 2+ release and uptake, and not I f , were responsible for spontaneous beating in NRM and hiPS-CM. Ca 2+ signaling parameters of hiPS-CM were also similar to those of adult atrial myocytes with Ca 2+ currents averaging ~8 pA/pF and I Ca -induced Ca 2+ -transients having a bell-shaped voltage-dependence similar to that of I Ca , consistent with Ca 2+ -induced Ca 2+ -release (CICR) mechanism. The ratio of I Ca -activated to caffeine-triggered Ca 2+ -transients was ~0.3, similar to the value in rat atria, but significantly smaller than the value of >0.8 in ventricle. The gain of CICR was voltage-dependent as in adult cardiomyocytes. Adrenergic agonists enhanced I Ca , but elevated diastolic Ca 2+ . Ca 2+ -sparks were sporadic and brief in duration (< 25ms). Our data suggest that hiPS-CM have all the specific characteristics of adult cardiomyocytes and the mechanisms of their spontaneous pacing are similar to those found in NRM, and involve Ca 2+ cross-talk between NCX, RyR/SR, and possibly mitochondria.

Inhibition of Na+/H+exchange stimulates CCK secretion in STC-1 cells

1998 ◽  
Vol 275 (4) ◽  
pp. G689-G695
Author(s):  
Veronica Prpic ◽  
J. Gregory Fitz ◽  
Yu Wang ◽  
John R. Raymond ◽  
Maria N. Garnovskaya ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Cell Metabolism ◽  
Hormone Secretion ◽  
Membrane Depolarization ◽  
Ph Sensitive ◽  
Extracellular Medium ◽  
Voltage Dependent ◽  
Effects Of Ph ◽  
Intracellular Ca ◽  
Cck Release

It has been demonstrated that K+ channel regulation of membrane potential is critical for control of CCK secretion. Because certain K+ channels are pH sensitive, it was postulated that pH affects K+channel activity in the CCK-secreting cell line STC-1 and may participate in regulating CCK secretion. The present study examines the role of electroneutral Na+/H+exchange on extracellular acidification and hormone secretion. Treatment of STC-1 cells with the amiloride analog ethylisopropyl amiloride (EIPA) to inhibit Na+/H+exchange inhibited Na+-dependent H+ efflux and increased basal CCK secretion. Substituting choline for NaCl in the extracellular medium elevated basal intracellular Ca2+concentration and stimulated CCK release. Stimulatory effects on hormone secretion were blocked by the L-type Ca2+ channel blocker diltiazem, indicating that secretion was dependent on the influx of extracellular Ca2+. To determine whether the effects of EIPA and Na+ depletion were due to membrane depolarization, we tested graded KCl concentrations. The ability of EIPA to increase CCK secretion was inhibited by depolarization induced by 10–50 mM KCl in the bath. Maneuvers to lower intracellular pH (pHi), including reducing extracellular pH (pHo) to 7.0 or treatment with sodium butyrate, significantly increased CCK secretion. To examine whether pH directly affects membrane K+ permeability, we measured outward currents carried by K+, using whole cell patch techniques. K+ current was significantly inhibited by lowering pHo to 7.0. These effects appear to be mediated through changes in pHi, because intracellular dialysis with acidic solutions nearly eliminated current activity. These results suggest that Na+/H+exchange and membrane potential may be functionally linked, where inhibition of Na+/H+exchange lowers pHi and depolarizes the membrane, perhaps through inhibition of pH-sensitive K+ channels. In turn, K+ channel closure and membrane depolarization open voltage-dependent Ca2+ channels, leading to an increase in cytosolic Ca2+ and CCK release. The effects of pHi on K+ channels may serve as a potent stimulus for hormone secretion, linking cell metabolism and secretory functions.

scholarly journals NK2 receptor-mediated detrusor muscle contraction involves Gq/11-dependent activation of voltage-dependent Ca2+ channels and the RhoA-Rho kinase pathway

2019 ◽  
Vol 317 (5) ◽  
pp. F1154-F1163 ◽  
Author(s):  
Bálint Dér ◽  
Péter József Molnár ◽  
Éva Ruisanchez ◽  
Petra Őrsy ◽  
Margit Kerék ◽  
...  
Keyword(s):  
Urinary Bladder ◽  
Rho Kinase ◽  
Detrusor Muscle ◽  
Dependent Manner ◽  
Contraction Force ◽  
Rhoa Activity ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
Nk2 Receptor ◽  
Kinase Pathway

Tachykinins (TKs) are involved in both the physiological regulation of urinary bladder functions and development of overactive bladder syndrome. The aim of the present study was to investigate the signal transduction pathways of TKs in the detrusor muscle to provide potential pharmacological targets for the treatment of bladder dysfunctions related to enhanced TK production. Contraction force, intracellular Ca2+ concentration, and RhoA activity were measured in the mouse urinary bladder smooth muscle (UBSM). TKs and the NK2 receptor (NK2R)-specific agonist [β-Ala8]-NKA(4–10) evoked contraction, which was inhibited by the NKR2 antagonist MEN10376. In Gαq/11-deficient mice, [β-Ala8]-NKA(4–10)-induced contraction and the intracellular Ca2+ concentration increase were abolished. Although Gq/11 proteins are linked principally to phospholipase Cβ and inositol trisphosphate-mediated Ca2+ release from intracellular stores, we found that phospholipase Cβ inhibition and sarcoplasmic reticulum Ca2+ depletion failed to have any effect on contraction induced by [β-Ala8]-NKA(4–10). In contrast, lack of extracellular Ca2+ or blockade of voltage-dependent Ca2+ channels (VDCCs) suppressed contraction. Furthermore, [β-Ala8]-NKA(4–10) increased RhoA activity in the UBSM in a Gq/11-dependent manner and inhibition of Rho kinase with Y-27632 decreased contraction force, whereas the combination of Y-27632 with either VDCC blockade or depletion of extracellular Ca2+ resulted in complete inhibition of [β-Ala8]-NKA(4–10)-induced contractions. In summary, our results indicate that NK2Rs are linked exclusively to Gq/11 proteins in the UBSM and that the intracellular signaling involves the simultaneous activation of VDCC and the RhoA-Rho kinase pathway. These findings may help to identify potential therapeutic targets of bladder dysfunctions related to upregulation of TKs.

Parathyroid cells express dihydropyridine-sensitive cation currents and L-type calcium channel subunits

2001 ◽  
Vol 281 (1) ◽  
pp. E180-E189 ◽  
Author(s):  
Wenhan Chang ◽  
Stacy A. Pratt ◽  
Tsui-Hua Chen ◽  
Chia-Ling Tu ◽  
Gabor Mikala ◽  
...  
Keyword(s):  
Parathyroid Hormone ◽  
Northern Blot ◽  
Northern Blot Analysis ◽  
Inhibitory Effects ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
Alternatively Spliced ◽  
Induced Changes ◽  
Spliced Variant ◽  
Cdna Fragments

Parathyroid cells express Ca2+-conducting currents that are activated by raising the extracellular Ca2+ concentration ([Ca2+]o). We investigated the sensitivity of these currents to dihydropyridines, the expression of voltage-dependent Ca2+ channel (VDCC) subunits, and the effects of dihydropyridines on the intracellular free [Ca2+] ([Ca2+]i) and secretion in these cells. Dihydropyridine channel antagonists dose dependently suppressed Ca2+-conducting currents, and agonists partially reversed the inhibitory effects of the antagonists in these cells. From a bovine parathyroid cDNA library, we isolated cDNA fragments encoding parts of an α1S- and a β3-subunit of L-type Ca2+ channels. The α1S-subunit cDNA from the parathyroid represents an alternatively spliced variant lacking exon 29 of the corresponding gene. Northern blot analysis and immunocytochemistry confirmed the presence of transcripts and proteins for α1- and β3-subunits in the parathyroid gland. The addition of dihydropyridines had no significant effects on high [Ca2+]o-induced changes in [Ca2+]i and parathyroid hormone (PTH) release. Thus our studies indicate that parathyroid cells express alternatively spliced L-type Ca2+ channel subunits, which do not modulate acute intracellular Ca2+ responses or changes in PTH release.

Bombesin-evoked gastrin release and calcium signaling in human antral G cells in culture

1999 ◽  
Vol 276 (1) ◽  
pp. G227-G237 ◽  
Author(s):  
Paul E. Squires ◽  
R. Mark Meloche ◽  
Alison M. J. Buchan
Keyword(s):  
Cell Culture ◽  
Calcium Signaling ◽  
Gastrin Release ◽  
Voltage Gated ◽  
Gastrin Releasing Peptide ◽  
G Cells ◽  
Peptide Family ◽  
Inositol 1,4,5 Trisphosphate ◽  
Voltage Dependent ◽  
Intracellular Ca

Amplification of mRNA from a human antral cell culture preparation demonstrated the presence of two receptors of the bombesin and gastrin-releasing peptide family, GRPR-1 and BRS-3. Single cell microfluorometry demonstrated that most cells that exhibited bombesin-evoked changes in intracellular Ca2+ concentration were gastrin immunoreactive, indicating that antral G cells express the GRPR subtype. There were two components to the intracellular Ca2+ response: an initial nitrendipine-insensitive mobilization followed by a sustained phase that was inhibited by removal of extracellular Ca2+ and 20 mM caffeine and was partially inhibited by 10 μM nitrendipine. Preexposure of cells to thapsigargin and caffeine prevented the response to bombesin, indicating activation of inositol 1,4,5-trisphosphate (IP3)-sensitive stores. Gastrin release could be partially reversed by removal of extracellular Ca2+ and blockade of L-type voltage-dependent Ca2+ channels, indicating that a component of the secretory response to bombesin was dependent on Ca2+ influx. These data demonstrated that bombesin-stimulated gastrin release from human antral G cells resulted from activation of GRPRs and involved both release of intracellular Ca2+ and influx of extracellular Ca2+through a combination of L-type voltage-gated and IP3-gated Ca2+ channels.

Ionic Mechanisms of Muscarinic Depolarization in Entorhinal Cortex Layer II Neurons

1997 ◽  
Vol 77 (4) ◽  
pp. 1829-1843 ◽  
Author(s):  
Ruby Klink ◽  
Angel Alonso
Keyword(s):  
Entorhinal Cortex ◽  
Cell Activity ◽  
Input Resistance ◽  
Receptor Activation ◽  
Dependent Manner ◽  
Tissue Slices ◽  
Voltage Range ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
Ionic Mechanisms

Klink, Ruby and Angel Alonso. Ionic mechanisms of muscarinic depolarization in entorhinal cortex layer II neurons. J. Neurophysiol. 77: 1829–1843, 1997. The mechanisms underlying direct muscarinic depolarizing responses in the stellate cells (SCs) and non-SCs of medial entorhinal cortex layer II were investigated in tissue slices by intracellular recording and pressure-pulse applications of carbachol (CCh). Subthreshold CCh depolarizations were largely potentiated in amplitude and duration when paired with a short DC depolarization that triggered cell firing. During Na+ conductance block, CCh depolarizations were also potentiated by a brief DC depolarization that allowed Ca2+ influx and the potentiation was more robust in non-SCs than in SCs. Also, in non-SCs, CCh depolarizations could be accompanied by spikelike voltage oscillations at a slow frequency. In both SCs and non-SCs, the voltage-current ( V-I) relations were similarly affected by CCh, which caused a shift to the left of the steady-state V-I relations over the entire voltage range and an increase in apparent slope input resistance at potentials positive to about −70 mV. CCh responses potentiated by Ca2+ influx demonstrated a selective increase in slope input resistance at potentials positive to about −75 mV in relation to the nonpotentiated responses. K+ conductance block with intracellular injection of Cs+ (3 M) and extracellular Ba2+ (1 mM) neither abolished CCh depolarizations nor resulted in any qualitatively distinct effect of CCh on the V-I relations. CCh depolarizations were also undiminished by block of the time-dependent inward rectifier I h with extracellular Cs+. However, CCh depolarizations were abolished during Ca2+ conductance block with low-Ca2+ (0.5 mM) solutions containing Cd2+, Co2+, or Mn2+, as well asby intracellular Ca2+ chelation with bis-( o-aminophenoxy)- N,N,N′,N′-tetraacetic acid. Inhibition of the Na+-K+ ATPase with strophanthidin resulted in larger CCh depolarizations. On the other hand, when NaCl was replaced by N-methyl-d-glucamine, CCh depolarizations were largely diminished. CCh responses were blocked by 0.8 μM pirenzepine, whereas hexahydro-sila-difenidolhydrochloride,p-fluoroanalog (p-F-HHSiD) and himbacine were only effective antagonists at 5- to 10-fold larger concentrations. Our data are consistent with CCh depolarizations being mediated in both SCs and non-SCs by m1 receptor activation of a Ca2+-dependent cationic conductance largely permeable to Na+. Activation of this conductance is potentiated in a voltage-dependent manner by activity triggering Ca2+ influx. This property implements a Hebbian-like mechanism whereby muscarinic receptor activation may only be translated into substantial membrane depolarization if coupled to postsynaptic cell activity. Such a mechanism could be highly significant in light of the role of the entorhinal cortex in learning and memory as well as in pathologies such as temporal lobe epilepsy.

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