Role of Rho-kinase in guinea-pig gallbladder smooth muscle contraction

Guinea-pig gallbladder smooth muscle contractions can be elicited pharmacologically by a range of mechanisms. The involvement of Rho-kinase in contractions mediated by receptor-dependent and receptor-independent mechanisms was investigated using the Rho-kinase inhibitor (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexane carboxamide (Y-27632). In a separate series of experiments, the role of Rho-kinase in the contractile response to Ca2+ entry through store-operated Ca2+ channels and to electrical field stimulation was also examined. Y-27632 (10 μM), which caused a significant decrease (P < 0.0005) in basal resting tone, significantly inhibited gallbladder contractions evoked by cumulative additions of the G-protein-coupled agonists, carbachol (1 nM–100 μM; P < 0.05) and cholecystokinin (10 nM–1 μM; P < 0.005). Y-27632 also inhibited the contractions evoked by a single addition of the sarcoplasmic reticulum ATPase inhibitor, thapsigargin (1 μM; P < 0.0005) and cumulative additions of KCl (10–85 mM; P < 0.0005). The contractile response to Ca2+ entry through store-operated Ca2+ channels was significantly inhibited by Y-27632 (P < 0.05) as were the contractile responses evoked by electrical field stimulation (2–25 Hz; P < 0.0005). In contrast, Y-27632 had no significant effect on contractions evoked by phorbol 12,13-dibutyrate (0.1 nM–1 μM; a protein kinase C activator) or by the phosphatase inhibitor, cantharidin (100 μM). In conclusion, Rho-kinase contributes to the contractile response in guinea-pig gallbladder smooth muscle evoked by both G-protein-coupled and non-G-protein-coupled mechanisms in addition to contributing to the maintenance of basal tone. It also contributes to the contractile responses resulting from electrical field stimulation and store-operated Ca2+ channel entry.