Role for G12/G13 in Agonist-Induced Vascular Smooth Muscle Cell Contraction

Abstract —Receptor-induced vascular smooth muscle cell contraction is mediated by dual regulation of myosin light chain (MLC20) phosphorylation through Ca2+-dependent stimulation of myosin light chain kinase and Rho/Rho-kinase–mediated inhibition of myosin phosphatase. Although myosin light chain kinase regulation is initiated by the coupling of receptors to G proteins of the Gq family, Gq and G11, it is not known how receptors regulate the Rho/Rho-kinase–mediated pathway. In vascular smooth muscle cells, receptor-mediated MLC20 phosphorylation and cell contraction was blocked by inhibitors of each of the pathways. Receptors of various vasocontractors were found to couple to Gq/G11 and G12/G13, and constitutively active forms of Gα12 and Gα13 induced a pronounced contraction of vascular smooth muscle cells that could be blocked by C3 exoenzyme, by inhibition of Rho-kinase, and by stable analogues of cGMP and cAMP. Receptor-mediated smooth muscle cell contraction was strongly inhibited by dominant-negative forms of Gα12 and Gα13. These data indicate that a G12/G13-mediated Rho/Rho-kinase–dependent pathway operates in smooth muscle cells and that dual regulation of MLC20 phosphorylation by vasocontractors is initiated by the dual coupling of their receptors to G proteins of the Gq and G12 families.