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

Abstract

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 [Ca ²⁺]_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.