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This Article Full Text Full Text (PDF) Supplemental Figures All Versions of this Article: 297/1/H191    most recent 00132.2009v1 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 PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Yuen, S. L. Articles by Brozovich, F. V. PubMed PubMed Citation Articles by Yuen, S. L. Articles by Brozovich, F. V.

Nonmuscle myosin is regulated during smooth muscle contraction

Cardiovascular Diseases, Mayo Medical School, Rochester, Minnesota

Submitted 9 February 2009 ; accepted in final form 5 May 2009

The participation of nonmuscle myosin in force maintenance is controversial. Furthermore, its regulation is difficult to examine in a cellular context, as the light chains of smooth muscle and nonmuscle myosin comigrate under native and denaturing electrophoresis techniques. Therefore, the regulatory light chains of smooth muscle myosin (SM-RLC) and nonmuscle myosin (NM-RLC) were purified, and these proteins were resolved by isoelectric focusing. Using this method, intact mouse aortic smooth muscle homogenates demonstrated four distinct RLC isoelectric variants. These spots were identified as phosphorylated NM-RLC (most acidic), nonphosphorylated NM-RLC, phosphorylated SM-RLC, and nonphosphorylated SM-RLC (most basic). During smooth muscle activation, NM-RLC phosphorylation increased. During depolarization, the increase in NM-RLC phosphorylation was unaffected by inhibition of either Rho kinase or PKC. However, inhibition of Rho kinase blocked the angiotensin II-induced increase in NM-RLC phosphorylation. Additionally, force for angiotensin II stimulation of aortic smooth muscle from heterozygous nonmuscle myosin IIB knockout mice was significantly less than that of wild-type littermates, suggesting that, in smooth muscle, activation of nonmuscle myosin is important for force maintenance. The data also demonstrate that, in smooth muscle, the activation of nonmuscle myosin is regulated by Ca²⁺-calmodulin-activated myosin light chain kinase during depolarization and a Rho kinase-dependent pathway during agonist stimulation.

Rho kinase; agonist; depolarization; myosin light chain kinase