Caffeine induces Ca2+ release by reducing the threshold for luminal Ca2+ activation of the ryanodine receptor
Open Access
- 27 August 2008
- journal article
- research article
- Published by Portland Press Ltd. in Biochemical Journal
- Vol. 414 (3), 441-452
- https://doi.org/10.1042/bj20080489
Abstract
Caffeine has long been used as a pharmacological probe for studying RyR (ryanodine receptor)-mediated Ca2+ release and cardiac arrhythmias. However, the precise mechanism by which caffeine activates RyRs is elusive. In the present study, we investigated the effects of caffeine on spontaneous Ca2+ release and on the response of single RyR2 (cardiac RyR) channels to luminal or cytosolic Ca2+. We found that HEK-293 cells (human embryonic kidney cells) expressing RyR2 displayed partial or ‘quantal’ Ca2+ release in response to repetitive additions of submaximal concentrations of caffeine. This quantal Ca2+ release was abolished by ryanodine. Monitoring of endoplasmic reticulum luminal Ca2+ revealed that caffeine reduced the luminal Ca2+ threshold at which spontaneous Ca2+ release occurs. Interestingly, spontaneous Ca2+ release in the form of Ca2+ oscillations persisted in the presence of 10 mM caffeine, and was diminished by ryanodine, demonstrating that unlike ryanodine, caffeine, even at high concentrations, does not hold the channel open. At the single-channel level, caffeine markedly reduced the threshold for luminal Ca2+ activation, but had little effect on the threshold for cytosolic Ca2+ activation, indicating that the major action of caffeine is to reduce the luminal, but not the cytosolic, Ca2+ activation threshold. Furthermore, as with caffeine, the clinically relevant, pro-arrhythmic methylxanthines aminophylline and theophylline potentiated luminal Ca2+ activation of RyR2, and increased the propensity for spontaneous Ca2+ release, mimicking the effects of disease-linked RyR2 mutations. Collectively, our results demonstrate that caffeine triggers Ca2+ release by reducing the threshold for luminal Ca2+ activation of RyR2, and suggest that disease-linked RyR2 mutations and RyR2-interacting pro-arrhythmic agents may share the same arrhythmogenic mechanism.Keywords
This publication has 58 references indexed in Scilit:
- Endoplasmic reticulum Ca2+ measurements reveal that the cardiac ryanodine receptor mutations linked to cardiac arrhythmia and sudden death alter the threshold for store-overload-induced Ca2+ releaseBiochemical Journal, 2008
- Luminal Ca2+ Regulation of Single Cardiac Ryanodine Receptors: Insights Provided by Calsequestrin and its MutantsThe Journal of general physiology, 2008
- Loss of luminal Ca 2+ activation in the cardiac ryanodine receptor is associated with ventricular fibrillation and sudden deathProceedings of the National Academy of Sciences, 2007
- Ca2+ Stores Regulate Ryanodine Receptor Ca2+ Release Channels via Luminal and Cytosolic Ca2+ SitesBiophysical Journal, 2007
- Skeletal and Cardiac Ryanodine Receptors Exhibit Different Responses to Ca2+ Overload and Luminal Ca2+Biophysical Journal, 2007
- Casq2 deletion causes sarcoplasmic reticulum volume increase, premature Ca2+ release, and catecholaminergic polymorphic ventricular tachycardiaJCI Insight, 2006
- Mice with the R176Q cardiac ryanodine receptor mutation exhibit catecholamine-induced ventricular tachycardia and cardiomyopathyProceedings of the National Academy of Sciences, 2006
- Stabilization of cardiac ryanodine receptor prevents intracellular calcium leak and arrhythmiasProceedings of the National Academy of Sciences, 2006
- Measurement of sarcoplasmic reticulum Ca2+ content and sarcolemmal Ca2+ fluxes in isolated rat ventricular myocytes during spontaneous Ca2+ releaseThe Journal of Physiology, 1997
- Reversal of acute theophylline toxicity by calcium channel blockers in dogs and ratsToxicology, 1996