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.
Schneider
M F
MF
Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore 21201, USA. mschneid@umabnet.ab.umd.edu
Klein
M G
MG
D000818:Animals; D002118:Calcium / Q000502:physiology*; D004594:Electrophysiology; D018613:Microscopy, Confocal; D018482:Muscle, Skeletal / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000502:physiology*
D002118:Calcium