Abstract
The C(superscript 2+)-dependent phosphorylation/dephosphorylation of myosin regulatory light chain by myosin light chain kinase (MLCK)/myosin light chain phosphatase is thought to control the contraction-relaxation cycle of smooth muscle. Smooth muscle myosin contains two heavy chains and two pairs of light chains, one 20-kD regulatory light chains (MRLC) and the other 17-kD essential light chains. Activation by Ca(superscript 2+)-calmodulin triggers MLCK to phosphorylate serine-19 and/or threonine-18 at MRLC so as to increase actin-activated myosin ATPase activity. Once phosphorylated, the myosin cross-bridges can bind to actin and generate force by cross-bridge cycling. Moreover, recent evidence has been provided that both thin filament regulation and actin filament dynamics are also involved in the control of smooth muscle contraction. Here, we focus attention on the potential roles of actin filament polymerization/depolymerization in smooth muscle.
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