Sarcomeric calcium sparks activated by fiber depolarization and by cytosolic Ca2+ in skeletal muscle.
Discrete highly localized elevations of myoplasmic [Ca2+], calcium 'sparks', have been detected in skeletal muscle fibers. During relatively small depolarizations of a fiber, the calcium sparks are several times larger than the average increase in [Ca2+] and can thus be clearly resolved. The spark event frequency increases steeply with increasing depolarization, so that for larger depolarizations the discrete microscopic [Ca2+] elevations blend together and become indistinguishable in the average macroscopic [Ca2+] transient. Spontaneous calcium sparks also occur in the absence of voltage sensor activity, in which case they are activated by myoplasmic Ca2+. Both the voltage-activated and Ca(2+)-activated events originate at the location of the triad within the sarcomere. Calcium sparks appear to constitute the elementary unit of calcium release activation in skeletal muscle.
Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore 21201, USA. mschneid@umabnet.ab.umd.edu
M F
MF
Schneider
M G
MG
Klein
D000818:Animals; D002118:Calcium / Q000502:physiology*; D004594:Electrophysiology; D018613:Microscopy, Confocal; D018482:Muscle, Skeletal / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000502:physiology*
D002118:Calcium