Caffeine-induced Ca(2+) sparks in mouse ventricular myocytes.
Ca(2+) sparks are spatially localized intracellular Ca(2+) release events that were first described in 1993. Sparks have been ascribed to sarcoplasmic reticulum Ca(2+) release channel (ryanodine receptor, RyR) opening induced by Ca(2+) influx via L-type Ca(2+) channels or by spontaneous RyR openings and have been thought to reflect Ca(2+) release from a cluster of RyR. Here we describe a pharmacological approach to study sparks by exposing ventricular myocytes to caffeine with a rapid solution-switcher device. Sparks under these conditions have properties similar to naturally occurring sparks in terms of size and intracellular Ca(2+) concentration ([Ca(2+)](i)) amplitude. However, after the diffusion of caffeine, sparks first appear close to the cell surface membrane before coalescing to produce a whole cell transient. Our results support the idea that a whole cell [Ca(2+)](i) transient consists of the summation of sparks and that Ca(2+) sparks consist of the opening of a cluster of RyR and confirm that characteristics of the cluster rather than the L-type Ca(2+) channel-RyR relation determine spark properties.
Ritter
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Division of Cardiology, University of Utah Health Sciences Center, Salt Lake City, Utah 84132, USA.
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Spitzer
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Ishida
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Barry
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D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D005260:Female; D005456:Fluorescent Dyes; D006352:Heart Ventricles; D007425:Intracellular Membranes / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*
D005456:Fluorescent Dyes; D002110:Caffeine; D002118:Calcium