Key result
Modulation of MLC20 phosphorylation demonstrated that phosphorylated myosin triggers actin polymerization and enhances force development in arterial smooth muscle.
This study demonstrates that myosin phosphorylation triggers actin polymerization in vascular smooth muscle, suggesting that myosin binding to actin enhances force development.
Findings in animal models extend mechanistic insight into arterial force generation; leaves open translation to human vascular disease.
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 beta-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 beta-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.
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Chen et al. (2008) studied this question. MLC kinase inhibition with ML-7 or myosin light chain phosphatase inhibition with microcystin was evaluated on Isometric force, degree of actin polymerization (F-actin-to-G-actin ratio), and MLC20 phosphorylation. Modulation of MLC20 phosphorylation demonstrated that phosphorylated myosin triggers actin polymerization and enhances force development in arterial smooth muscle.
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