Inhibition of Rho-associated kinase reduces MLC20 phosphorylation and contractility of intact myometrium and attenuates agonist-induced Ca2+ Sensitization of force of permeabilized rat myometrium

The role of rhoA/rho-associated kinase (ROK) signaling pathways in agonist-induced contraction of the rat myometrium was investigated. We measured the [Ca2+](i)-force relationship, phosphorylation of myosin regulatory light chains (MLC20) in intact tissue and the Ca2+-sensitization of force in permeabilized myometrial cells of rat. In measurements of the relationship between [Ca2+](i) and tension in intact tissue, Y-27632, a ROK inhibitor, significantly attenuated the carbachol-induced contraction without changing [Ca2+](i). Phosphorylation of MLC20 was increased by carbachol and this increased phosphorylation was blocked by treatment of tissue with Y-27632. In tension measurements of single hyperpermeable cells, carbachol evoked sustained contraction at constant pCa 6.7 and these agonist-induced contractions were decreased by treatment with Y-27632. These results suggest that activation of a ROK-mediated signaling pathway(s) plays an important role in agonist-induced alterations in MLC20 phosphorylation and force of rat myometrium.