title: Calcium-induced calcium release in smooth muscle: the case for loose coupling.
abstract: This article reviews the key experiments demonstrating calcium-induced calcium release (CICR) in smooth muscle and contrasts the biophysical and molecular features of coupling between the sarcolemmal (L-type Ca(2+) channel) and sarcoplasmic reticulum (ryanodine receptor) Ca(2+) channels in smooth and cardiac muscle. Loose coupling refers to the coupling process in smooth muscle in which gating of ryanodine receptors is non-obligate and may occur with a variable delay following opening of the sarcolemmal Ca(2+) channels. These features have been observed in the earliest studies of CICR in smooth muscle and are in marked contrast to cardiac CICR, where a close coupling between T-tubular and SR membranes results in tight coupling between the gating events. The relationship between this "loose coupling" and distinct subcellular release sites within smooth muscle cells, termed frequent discharge sites, is discussed.
authors.affiliation: College of Veterinary Medicine, Cornell University, T4 018 VRT, Box 11, Ithaca, NY 14853-6401, USA. mik7@cornell.edu
authors.forename: Michael I
authors.initials: MI
authors.lastname: Kotlikoff
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology; D002478:Cells, Cultured; D006801:Humans; D009130:Muscle, Smooth / Q000737:chemistry / Q000378:metabolism*; D009206:Myocardium / Q000737:chemistry / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D019837:Ryanodine Receptor Calcium Release Channel / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D020746:Calcium Channels, L-Type; D019837:Ryanodine Receptor Calcium Release Channel; D002118:Calcium