Smooth muscle contraction follows an increase in cytosolic Ca 2+ concentration, activation
of myosin light chain kinase, and phosphorylation of the 20-kDa light chain of myosin at Ser
19. Several agonists acting via G protein-coupled receptors elicit a contraction without a
change in [Ca 2+] i via inhibition of myosin light chain phosphatase and increased myosin
phosphorylation. We showed that microcystin (phosphatase inhibitor)-induced contraction of
skinned smooth muscle occurred in the absence of Ca 2+ and correlated with …