Myosin triggers actin polymerization in vascular smooth muscle

Abstract

Actin polymerization is a dynamic process, which plays an essential role in smooth muscle contraction. In vitro studies have suggested that myosin alone increases actin polymerization. The present study examined the effects of myosin on actin polymerization in isolated arteries. These studies were conducted in both intact and β-escin permeabilized small mesenteric arteries. Actin polymerization was determined by F/G-actin ratio and myosin light chain phosphorylation was detected by western blot. Isometric contractile function of the vessels was measured on a wire myograph. The myosin light chain kinase inhibitor, ML-7, and the myosin light chain phosphatase inhibitor, microcystin, were used to modulate myosin light chain phosphorylation. By correlating myosin light chain phosphorylation with actin polymerization, we demonstrated that type II myosin light chain phosphorylation is necessary for increasing actin polymerization in smooth muscle. We further demonstrated that the introduction of the actin-binding domain of the myosin head into permeabilized vessels increased microcystin-induced force development and actin polymerization. We conclude that myosin phosphorylation triggers actin polymerization in vascular smooth muscle. (Supported by NIDDK-51430)