Regulation of a Smooth Muscle Contraction: A Hypothesis Based on Skinned Fiber Studies
Although it is generally believed that smooth muscle will contract in response to an increase in cytosolic free calcium ion concentration, there is still considerable controversy concerning the explicit mechanism(s) coupling calcium to contraction. Bremel (1974), using filament displacement studies, showed that the Ca2+ dependence of vertebrate smooth muscle contraction is associated primarily with the thick filament. A few years later, Aksoy et al. (1976) and Sobieszek (1977) demonstrated that the Ca2+ sensitivity of acto-myosin ATPase activity was associated with phosphorylation of the 20 kDa myosin light chain (MLC) which was subsequently shown to result from activation of MLC kinase, a Ca2+ and calmodulin dependent enzyme (for reviews see Kamm and Stull, 1985; Hartshorne, 1987). Correlations have been shown between MLC phosphorylation and both Ca2+ dependent actin-activated myosin ATPase activity (Dabrowska et al., 1978; DiSalvo et al., 1978) and force development in either skinned (Kerrick et al., 1980; Chatterjee and Murphy, 1983) or intact (Barron et al., 1980; Driska et al., 1981) muscle fibers. These findings have brought about the widespread belief that this system is the primary regulator of smooth muscle contraction.
KeywordsMyosin Light Chain Smooth Muscle Contraction Myosin Light Chain Phosphorylation Smooth Muscle Fiber Myosin Light Chain Phosphatase
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