Molecular aspects of arterial smooth muscle contraction: Focus on Rho

The vascular smooth muscle cell is a highly specialized cell whose primary function is contraction and relaxation. It expresses a variety of contractile proteins, ion channels, and signalling molecules that regulate contraction. Upon contraction, vascular smooth muscle cells shorten, thereby decreasing the diameter of a blood vessel to regulate the blood flow and pressure. Contractile activity in vascular smooth muscle cells is initiated by a Ca ²⁺-calmodulin interaction to stimulate phosphorylation of the light chain of myosin. Ca²⁺-sensitization of the contractile proteins is signaled by the RhoA/Rho-kinase pathway to inhibit the dephosphorylation of the light chain by myosin phosphatase, thereby maintaining force. Removal of Ca ²⁺ from the cytosol and stimulation of myoson phosphatase initiate the relaxation of vascular smooth muscle.