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This Article Full Text Full Text (PDF) All Versions of this Article: 295/5/H2172    most recent 91437.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Chen, X. Articles by Benoit, J. N. Search for Related Content PubMed PubMed Citation Articles by Chen, X. Articles by Benoit, J. N.

Myosin phosphorylation triggers actin polymerization in vascular smooth muscle

Department of Pharmacology, Physiology and Therapeutics, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota

Submitted 18 December 2007 ; accepted in final form 29 September 2008

A variety of contractile stimuli increases actin polymerization, which is essential for smooth muscle contraction. However, the mechanism(s) of actin polymerization associated with smooth muscle contraction is not fully understood. We tested the hypothesis that phosphorylated myosin triggers actin polymerization. The present study was conducted in isolated intact or β-escin-permeabilized rat small mesenteric arteries. Reductions in the 20-kDa myosin regulatory light chain (MLC₂₀) phosphorylation were achieved by inhibiting MLC kinase with ML-7. Increases in MLC₂₀ phosphorylation were achieved by inhibiting myosin light chain phosphatase with microcystin. Isometric force, the degree of actin polymerization as indicated by the F-actin-to-G-actin ratio, and MLC₂₀ phosphorylation were determined. Reductions in MLC₂₀ phosphorylation were associated with a decreased force development and actin polymerization. Increased MLC₂₀ phosphorylation was associated with an increased force generation and actin polymerization. We also found that a heptapeptide that mimics the actin-binding motif of myosin II enhanced microcystin-induced force generation and actin polymerization without affecting MLC₂₀ phosphorylation in β-escin-permeabilized vessels. Collectively, our data demonstrate that MLC₂₀ phosphorylation is capable of triggering actin polymerization. We further suggest that the binding of myosin to actin triggers actin polymerization and enhances the force development in arterial smooth muscle.

isometric force; β-escin; myosin light chain kinase; myosin light chain phosphatase; ML-7; microcystin