Abstract
On the Loose: Uncaging Ca2+-induced Ca2+ Release in Smooth Muscle
Highlights
Movement of Ca2+ from intracellular stores into the cytosol is an essential component of excitation–contraction coupling in muscle
Smooth muscle Ca2+ sparks, which result from a concerted opening of clusters of ryanodine receptor (RyR) (Blatter et al, 1997; Mejia-Alvarez et al, 1999), generate microdomains of elevated (>10 μM) Ca2+ without changing global intracellular Ca2+ concentrations (Nelson et al, 1995; Soeller and Cannell, 1997; Perez et al, 2001)
Perhaps related to the loose coupling between L-type Ca2+ channels and RyRs is the observation that the spatial distribution of Ca2+ sparks in smooth muscle, spontaneous and evoked, is not stochastic but rather is limited to discrete subcellular sites called “frequent discharge sites” (Gordienko et al, 1998)
Summary
Movement of Ca2+ from intracellular stores into the cytosol is an essential component of excitation–contraction coupling in muscle. The Ca2+ signal produced by a spark is tightly coupled to large-conductance Ca2+-activated K+ (BK) channels. This local increase in [Ca2+]i activates nearby RyRs (to cause the Ca2+ sparks) by the mechanism of CICR.
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