Two mechanisms of quantized calcium release in skeletal muscle.
Skeletal muscle uses voltage sensors in the transverse tubular membrane that are linked by protein-protein interactions to intracellular ryanodine receptors, which gate the release of calcium from the sarcoplasmic reticulum. Here we show, by using voltage-clamped single fibres and confocal imaging, that stochastic calcium-release events, visualized as Ca2+ sparks, occur in skeletal muscle and originate at the triad. Unitary triadic Ca(2+)-release events are initiated by the voltage sensor in a steeply voltage-dependent manner, or occur spontaneously by a mechanism independent of the voltage sensor. Large-amplitude events also occur during depolarization and consist of two or more unitary events. We propose a 'dual-control' model for discrete Ca2+ release events from the sacroplasmic reticulum that unifies diverse observations about Ca(2+)-signalling in frog skeletal muscle, and that may be applicable to other excitable cells.
Klein
M G
MG
Department of Biological Chemistry, University of Maryland School of Medicine, Baltimore 21201, USA.
Cheng
H
H
Santana
L F
LF
Jiang
Y H
YH
Lederer
W J
WJ
Schneider
M F
MF
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D066298:In Vitro Techniques; D008564:Membrane Potentials; D018482:Muscle, Skeletal / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011894:Rana pipiens
D002118:Calcium