Contribution of Rho-kinase in human gallbladder contractions.

Rho/Rho-kinase-mediated pathway has been involved in a variety of physiological processes, including Ca2+ sensitization, which enhances smooth muscle contraction. In this study, first of all we investigated the expression of Rho-kinase (ROCK-2) and then the role of this protein in the control of smooth muscle contraction in the isolated human gallbladder. For this purpose, we examined the effects of a selective Rho-kinase inhibitor, (+)- (R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride monohydrate (Y-27632, 10(-8)-3x10(-5) M) on carbachol (10(-8)-10(-4) M), cholecystokinin-8 (10(-8) M), endothelin-1 (10(-8) M), histamine (10(-5) M), neurokinin A (10(-7)-10(-6) M), 5-hydroxytryptamine (10(-6)-10(-5) M) and potassium chloride (KCl, 25-50 mM)-induced contractions as well as spontaneous contractile activity. Y-27632 (10(-5) M) significantly reduced 5-hydroxytryptamine, neurokinin A and KCl-induced contractions. Moreover, this Rho-kinase inhibitor (10(-8)-3x10(-5) M, cumulatively) relaxed the contractions produced by cholecystokinin-8, endothelin-1 and histamine in a concentration-dependent manner, being the pEC50 values for Y-27632 5.74+/-0.12, 5.33+/-0.09 and 5.95+/-0.18, respectively. Carbachol (10(-8)-10(-4) M) produced concentration-dependent contractions, which were also inhibited significantly by Y-27632. In addition, the spontaneous contractile activity was suppressed in the presence of Y-27632 (10(-6)-10(-5) M). Moreover, Western blot analysis has revealed that Rho-kinase is expressed in homogenates of the human gallbladder. Taken together, these results show that Rho-kinase is expressed in the human gallbladder, and it has an essential role in agonists and depolarization-induced contractions as well as spontaneous contractile activity.