scholarly journals Heterogeneity of calcium clock functions in dormant, dysrhythmically and rhythmically firing single pacemaker cells isolated from SA node

Cell Calcium ◽  
2018 ◽  
Vol 74 ◽  
pp. 168-179 ◽  
Author(s):  
Mary S. Kim ◽  
Alexander V. Maltsev ◽  
Oliver Monfredi ◽  
Larissa A. Maltseva ◽  
Ashley Wirth ◽  
...  
Keyword(s):  
Pacemaker Cells ◽  
Sa Node

Normal spontaneous firing of cardiac pacemaker cells is regulated by basal pkc delta activation

2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
T Vinogradova ◽  
K Tarasov ◽  
D Riordon ◽  
Y Tarasova ◽  
E Lakatta
Keyword(s):  
Protein Kinase ◽  
Cycle Length ◽  
Cardiac Pacemaker ◽  
Funding Source ◽  
Spontaneous Firing ◽  
Pacemaker Cells ◽  
Patch Clamp Technique ◽  
Sa Node ◽  
Pkc Delta ◽  
Pkc Isoforms

Abstract   The spontaneous beating rate of rabbit sinoatrial node cells (SANC) is regulated by local subsarcolemmal calcium releases (LCRs) from sarcoplasmic reticulum (SR). LCRs appear during diastolic depolarization (DD) and activate an inward sodium/calcium exchange current which increases DD rate and thus accelerates spontaneous SANC firing. High basal level of protein kinase A and calcium/calmodulin-dependent protein kinase II phosphorylation are required to sustain basal LCRs and normal spontaneous SANC firing. Recently we discovered that basal PKC activation is also obligatory for cardiac pacemaker function: inhibition of PKC activity by broad spectrum PKC inhibitors Bis I or calphostin C markedly suppressed SR calcium cycling and decreased or abolished spontaneous beating of freshly isolated rabbit SANC. Here we studied which PKC isoforms mediate PKC-dependent effects on cardiac pacemaker cell automaticity. The PKC superfamily consists of 3 major subgroups: conventional, novel and atypical. All PKC isoforms were detected at the RNA level (RT-qPCR) in the rabbit SA node and ventricle, and expression levels were comparable in both tissues. Expression of PKCβ, however, was markedly higher in the rabbit SA node, compared to other PKC isoenzymes in either tissue. We verified expression of conventional PKC (α, β) and novel PKC-delta at the protein level in SANC and ventricular myocytes (VM). Western blot confirmed RNA results, showing a 6-fold higher PKCβ protein abundance in SANC compared to VM. Expression of PKCα protein was similar in both cell types, while PKC-delta protein was more abundant in VM. To study whether PKCβ regulates spontaneous beating of SANC we employed selective inhibitor of conventional (α, β, gamma) PKC isoforms Go6976 (10 μmol/L), which had no effects on either LCR characteristics (confocal microscopy, calcium indicator Fluo-3AM) or spontaneous beating of freshly isolated rabbit SANC (perforated patch-clamp technique). Because selective PKC-delta inhibitors are not available, we explored effects of PKC-delta inhibition comparing effects of Go6976 (the inhibitor of conventional PKCs) and Go6983, which inhibits conventional PKCs and PKC-delta. In contrast to Go6976, Go6983 (5 μmol/L) markedly decreased the LCR size (from 7.1±0.4 to 4.5±0.3 μm) and number per each spontaneous cycle (from 1.3±0.1 to 0.8±0.1). It also markedly increased the LCR period (time from the prior AP-induced calcium transient to the subsequent LCR) which was paralleled by an increase in the spontaneous SANC cycle length. Rottlerin, another PKC-delta inhibitor, produced similar effects on LCR characteristics, and markedly and time-dependently decreased DD rate, leading to an increase in the spontaneous cycle length, and finally abrogated the spontaneous SANC firing. Thus, our data indicate that basal activity of PKC-delta, but not that of PKCβ, is essential for generation of LCRs and normal spontaneous firing of cardiac pacemaker cells. Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): Intramural Research Program, National Institute on Aging, National Institute of Health, USA

Electrotonic interactions in delayed propagation and block within the guinea pig SA node

1983 ◽  
Vol 245 (1) ◽  
pp. H7-H16 ◽  
Author(s):  
S. L. Lipsius
Keyword(s):  
Guinea Pig ◽  
Action Potential ◽  
Action Potential Duration ◽  
Progressive Increase ◽  
Pacemaker Cells ◽  
Sa Node ◽  
Transmembrane Potentials ◽  
Electrotonic Interactions ◽  
Rapid Pacing ◽  
Exit Block

The influence of electrotonic interactions on propagation within the SA node was studied by recording transmembrane potentials simultaneously from two neighboring (less than 1 mm apart) subsidiary pacemaker cells within the sinoatrial (SA) node of the guinea pig. As single premature stimuli were delivered progressively earlier in diastole, retrograde propagation between cells was delayed progressively. Cells activated earlier displayed secondary depolarizations that were coincident with the depolarization of neighboring cells activated later. The secondary depolarizations increased action potential duration markedly. Rapid pacing elicited secondary depolarizations that resulted in a progressive increase in action potential duration and decrease in upstroke amplitude. These changes were associated with a progressive delay in retrograde propagation that led to intermittent block with Wenckebach periodicity. Exposure to tetrodotoxin (10(-5) g/ml) delayed antegrade propagation, resulting in electrotonically mediated secondary depolarizations and exit block with Wenckebach periodicity. It is concluded that delayed activation and electrotonically mediated interactions between cells can increase action potential duration and refractoriness. These changes contribute to progressive delays in propagation that may result in intermittent block with Wenckebach periodicity within the SA node.

scholarly journals Electrophysiological heterogeneity of pacemaker cells in the rabbit intercaval region, including the SA node: insights from recording multiple ion currents in each cell

2018 ◽  
Vol 314 (3) ◽  
pp. H403-H414 ◽  
Author(s):  
Oliver Monfredi ◽  
Kenta Tsutsui ◽  
Bruce Ziman ◽  
Michael D. Stern ◽  
Edward G. Lakatta ◽  
...  
Keyword(s):  
Ion Currents ◽  
Pacemaker Cells ◽  
Sa Node

Heterogeneity of 4-aminopyridine-sensitive current in rabbit sinoatrial node cells

1999 ◽  
Vol 276 (4) ◽  
pp. H1295-H1304 ◽  
Author(s):  
Haruo Honjo ◽  
Ming Lei ◽  
Mark R. Boyett ◽  
Itsuo Kodama
Keyword(s):  
Membrane Potential ◽  
Regional Differences ◽  
Sinoatrial Node ◽  
Pacemaker Cells ◽  
Electrophysiological Properties ◽  
Sa Node ◽  
Slope Factor ◽  
Ionic Mechanisms ◽  
Rabbit Sinoatrial Node ◽  
Cell Capacitance

The electrophysiological properties of sinoatrial (SA) node pacemaker cells vary in different regions of the node. In this study, we have investigated variation of the 4-aminopyridine (4-AP)-sensitive current as a function of the size (as measured by the cell capacitance) of SA node cells to elucidate the ionic mechanisms. The 10 mM 4-AP-sensitive current recorded from rabbit SA node cells was composed of transient and sustained components ( I trans and I sus, respectively). The activation and inactivation properties [activation: membrane potential at which conductance is half-maximally activated ( V h) = 19.3 mV, slope factor ( k) = 15.0 mV; inactivation: V h= −31.5 mV, k = 7.2 mV] as well as the density of I trans (9.0 pA/pF on average at +50 mV) were independent of cell capacitance. In contrast, the density of I sus (0.97 pA/pF on average at +50 mV) was greater in larger cells, giving rise to a significant correlation with cell capacitance. The greater density of I sus in larger cells (presumably from the periphery) can explain the shorter action potential in the periphery of the SA node compared with that in the center. Thus variation of the 4-AP-sensitive current may be involved in regional differences in repolarization within the SA node.

Diastolic SR Ca efflux in atrial pacemaker cells and Ca-overloaded myocytes

1997 ◽  
Vol 273 (2) ◽  
pp. H886-H892 ◽  
Author(s):  
R. A. Bassani ◽  
J. W. Bassani ◽  
S. L. Lipsius ◽  
D. M. Bers
Keyword(s):  
Spontaneous Activity ◽  
Ventricular Myocytes ◽  
Cardiac Cells ◽  
Transport Systems ◽  
Pacemaker Activity ◽  
Pacemaker Cells ◽  
Sa Node ◽  
Ca Uptake ◽  
Rabbit Ventricular Myocytes ◽  
Ca Depletion

Evidence has shown that the sarcoplasmic reticulum (SR) of cardiac cells releases Ca not only during excitation-contraction coupling but also during diastole, albeit at a much lower rate. This diastolic SR Ca release (leak) has also been implicated in the generation of spontaneous depolarization in latent atrial pacemaker cells of the cat right atrium. In the present work, we sought to measure Ca transients in pacemaker and nonpacemaker cells of the cat using the fluorescent Ca indicator indo 1. Atrial latent pacemaker cells develop a slow Ca transient when rested in the presence of both Na- and Ca-free solution and thapsigargin [used to inhibit Na/Ca exchange and SR Ca adenosinetriphosphatase (Ca-ATPase), respectively]. This increase in cytosolic Ca concentration ([Ca]i) is probably caused by the rate of SR Ca leak exceeding the capacity of the remaining Ca transport systems (e.g., sarcolemmal Ca-ATPase and mitochondrial Ca uptake). However, neither cat sinoatrial (SA) node cells nor myocytes from cat atrium or ventricle exhibited a similar increase in [Ca]i during the same protocol. This indicates that SR Ca leak in these cells occurred at a rate low enough to be within the capacity of the slow Ca transporters, as observed previously in rabbit ventricular myocytes. When atrial and ventricular myocytes were stimulated at higher frequencies, sufficient to markedly increase diastolic and systolic [Ca]i and approach Ca overload (and spontaneous activity), they responded to inhibition of SR Ca-ATPase and Na/Ca exchange with a slow Ca transient similar to that normally observed in atrial latent pacemaker cells. Furthermore, the SR Ca depletion by thapsigargin did not affect spontaneous activity of SA node cells, but it prevented or slowed pacemaker activity in the atrial latent pacemaker cells. These findings suggest that enhanced diastolic SR Ca efflux contributes significantly to the generation of spontaneous activity in atrial subsidiary pacemakers under normal conditions and in Ca-overloaded myocytes but not in SA node cells.

Sign in / Sign up

Export Citation Format

Share Document