Myosin light chain phosphorylation machinery

The myosin light chain (MLC) phosphorylation machinery in vascular smooth muscle is a fundamental regulatory system that controls vascular tone and blood pressure. This machinery operates through a balance between Myosin Light Chain Kinase (MLCK), which phosphorylates the 20-kDa regulatory light chain (MLC20) to initiate contraction, and Myosin Light Chain Phosphatase (MLCP), which dephosphorylates it to promote relaxation (Webb, 2003). The system is further modulated by the RhoA/ROCK signaling pathway, where Rho-associated protein kinase (ROCK) inhibits MLCP, leading to increased MLC20 phosphorylation and sustained vasoconstriction even at constant calcium levels, a phenomenon known as calcium sensitization (Somlyo & Somlyo, 2003). Dysregulation of this machinery, particularly through the overactivation of ROCK, is implicated in the pathogenesis of various cardiovascular and ocular diseases, including hypertension, coronary vasospasm, and glaucoma (Shimokawa & Rashid, 2007). Pharmacological targeting of this machinery, primarily through ROCK inhibitors like Fasudil and Netarsudil, has proven effective in inducing vasodilation and lowering intraocular pressure. These drugs work by shifting the equilibrium of the machinery toward the dephosphorylated state of myosin, thereby alleviating pathological vasoconstriction (Grassie et al., 2011).

Other names

MLC phosphorylation pathwayMyosin light chain kinase/phosphatase systemRhoA/ROCK/MLC signaling axisCalcium sensitization machinery

Inhibition of Rho-associated protein kinase (ROCK) or Myosin Light Chain Kinase (MLCK) to reduce the phosphorylation of the 20-kDa regulatory myosin light chain (MLC20), thereby promoting smooth muscle relaxation and vasodilation.