Localized intracellular calcium signaling in muscle: calcium sparks and calcium quarks.
Subcellularly localized Ca2+ signals in cardiac and skeletal muscle have recently been identified as elementary Ca2+ signaling events. The signals, termed Ca2+ sparks and Ca2+ quarks, represent openings of Ca2+ release channels located in the membrane of the sarcoplasmic reticulum (SR). In cardiac muscle, the revolutionary discovery of Ca2+ sparks has allowed the development of a fundamentally different concept for the amplification of Ca2+ signals by Ca(2+)-induced Ca2+ release. In such a system, a graded amplification of the triggering Ca2+ signal entering the myocyte via L-type Ca2+ channels is accomplished by a recruitment process whereby individual SR Ca2+ release units are locally controlled by L-type Ca2+ channels. In skeletal muscle, the initial SR Ca2+ release is governed by voltage-sensors but subsequently activates additional Ca2+ sparks by Ca(2+)-induced Ca2+ release from the SR. Results from studies on elementary Ca2+ release events will improve our knowledge of muscle Ca2+ signaling at all levels of complexity, from the molecule to normal cellular function, and from the regulation of cardiac and skeletal muscle force to the pathophysiology of excitation-contraction coupling.
Niggli
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Department of Physiology, University of Bern, Switzerland. niggli@pyl.unibe.ch
D000818:Animals; D002118:Calcium / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D007425:Intracellular Membranes / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism; D009132:Muscles / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism
D002118:Calcium