Termination of Ca2+ release by a local inactivation of ryanodine receptors in cardiac myocytes

J. S K Sham, L. S. Song, Ye Chen-Izu, L. H. Deng, M. D. Stern, E. G. Lakatta, H. Cheng

Research output: Contribution to journalArticle

138 Scopus citations

Abstract

In heart, a robust regulatory mechanism is required to counteract the regenerative Ca2+-induced Ca2+ release from the sarcoplasmic reticulum. Several mechanisms, including inactivation, adaptation, and stochastic closing of ryanodine receptors (RyRs) have been proposed, but no conclusive evidence has yet been provided. We probed the termination process of Ca2+ release by using a technique of imaging local Ca2+ release, or 'Ca2+ spikes', at subcellular sites; and we tracked the kinetics of Ca2+ release triggered by L-type Ca2+ channels. At 0 mV, Ca2+ release occurred and terminated within 40 ms after the onset of clamp pulses (0 mV). Increasing the open-duration and promoting the reopenings of Ca2+ channels with the Ca2+ channel agonist, FPL64176, did not prolong or trigger secondary Ca2+ spikes, even though two-thirds of the sarcoplasmic reticulum Ca2+ remained available for release. Latency of Ca2+ spikes coincided with the first openings but not with the reopenings of L-type Ca2+ channels. After an initial maximal release, even a multi-fold increase in unitary Ca2+ current induced by a hyperpolarization to -120 mV failed to trigger additional release, indicating absolute refractoriness of RyRs. When the release was submaximal (e.g., at +30 mV), tail currents did activate additional Ca2+ Spikes; confocal images revealed that they originated from RyRS unfired during depolarization. These results indicate that Ca2+ release is terminated primarily by a highly localized, use-dependent inactivation of RyRs but not by the stochastic closing or adaptation of RyRs in intact ventricular myocytes.

Original languageEnglish (US)
Pages (from-to)15096-15101
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume95
Issue number25
DOIs
StatePublished - 1998
Externally publishedYes

ASJC Scopus subject areas

  • Genetics
  • General

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