biostudies-literatureKong CHTAuckland Medical Research FoundationBritish Heart FoundationUniversity of BristolMedical Research CouncilRoyal SocietyHealth Research Council of New Zealand44-53https://www.ebi.ac.uk/biostudies/studies/S-EPMC7616665biostudies-literatureUnknown182Cardiac excitation-contraction coupling (ECC) depends on Ca²⁺ release from intracellular stores via ryanodine receptors (RyRs) triggered by L-type Ca²⁺ channels (LCCs). Uncertain numbers of RyRs and LCCs form 'couplons' whose activation produces Ca²⁺ sparks, which summate to form a cell-wide Ca²⁺ transient that switches on contraction. Voltage (V_m) changes during the action potential (AP) and stochasticity in channel gating should create variability in Ca²⁺ spark timing, but Ca²⁺ transient wavefronts have remarkable uniformity. To examine how this is achieved, we measured the V_m-dependence of evoked Ca²⁺ spark probability (P_spark) and latency over a wide voltage range in rat ventricular cells. With depolarising steps, Ca²⁺ spark latency showed a U-shaped V_m-dependence, while repolarising steps from 50 mV produced Ca²⁺ spark latencies that increased monotonically with V_m. A computer model based on reported channel gating and geometry reproduced our experimental data and revealed a likely RyR:LCC stoichiometry of ∼ 5:1 for the Ca²⁺ spark initiating complex (IC). Using the experimental AP waveform, the model revealed a high coupling fidelity (P_cpl ∼ 0.5) between each LCC opening and IC activation. The presence of ∼ 4 ICs per couplon reduced Ca²⁺ spark latency and increased P_spark to match experimental data. Variability in AP release timing is less than that seen with voltage steps because the AP overshoot and later repolarization decrease P_spark due to effects on LCC flux and LCC deactivation respectively. This work provides a framework for explaining the V_m- and time-dependence of P_spark, and indicates how ion channel dispersion in disease can contribute to dyssynchrony in Ca²⁺ release.Journal of molecular and cellular cardiologyCa<sup>2+</sup> spark latency and control of intrinsic Ca<sup>2+</sup> release dyssynchrony in rat cardiac ventricular muscle cells.PMC761666581,216FS/CRTF/21/24122IG/13/3/30212MR/N002903/1PG/20/5/3480108/049Kong CHTCannell MBfalseCa<sup>2+</sup> spark latency and control of intrinsic Ca<sup>2+</sup> release dyssynchrony in rat cardiac ventricular muscle cells.Cardiac excitation-contraction coupling (ECC) depends on Ca²⁺ release from intracellular stores via ryanodine receptors (RyRs) triggered by L-type Ca²⁺ channels (LCCs). Uncertain numbers of RyRs and LCCs form 'couplons' whose activation produces Ca²⁺ sparks, which summate to form a cell-wide Ca²⁺ transient that switches on contraction. Voltage (V_m) changes during the action potential (AP) and stochasticity in channel gating should create variability in Ca²⁺ spark timing, but Ca²⁺ transient wavefronts have remarkable uniformity. To examine how this is achieved, we measured the V_m-dependence of evoked Ca²⁺ spark probability (P_spark) and latency over a wide voltage range in rat ventricular cells. With depolarising steps, Ca²⁺ spark latency showed a U-shaped V_m-dependence, while repolarising steps from 50 mV produced Ca²⁺ spark latencies that increased monotonically with V_m. A computer model based on reported channel gating and geometry reproduced our experimental data and revealed a likely RyR:LCC stoichiometry of ∼ 5:1 for the Ca²⁺ spark initiating complex (IC). Using the experimental AP waveform, the model revealed a high coupling fidelity (P_cpl ∼ 0.5) between each LCC opening and IC activation. The presence of ∼ 4 ICs per couplon reduced Ca²⁺ spark latency and increased P_spark to match experimental data. Variability in AP release timing is less than that seen with voltage steps because the AP overshoot and later repolarization decrease P_spark due to effects on LCC flux and LCC deactivation respectively. This work provides a framework for explaining the V_m- and time-dependence of P_spark, and indicates how ion channel dispersion in disease can contribute to dyssynchrony in Ca²⁺ release.2023-01-01T00:00:00Z2023 Sep2025-04-04T08:21:27.848Z2025-04-04T08:21:27.848ZS-EPMC76166653743339110.1016/j.yjmcc.2023.07.005