The role of Rho and Rho-dependent kinase in serotonin-induced contraction observed in bovine middle cerebral artery

The current study was designed to characterize the role of Rho and Rho-dependent kinase (Rho-kinase) in isometric contractile responses induced by serotonin (5-HT) and a solution containing 40 mM K⁺ (high K⁺) in ring preparations of the middle cerebral artery of bovine. Application of W-7, a Ca²⁺-calmodulin inhibitor, reversibly and equally attenuated the amplitudes of contractions produced by both 5-HT and high K⁺. Similar effects were observed with ML-7, an inhibitor of myosin light chain kinase. Surprisingly, the protein kinase C inhibitors, calphostin C and Ro-31-8220, had no effect on the 5-HT-induced contraction. Incubation of preparations with Clostridium difficile toxin A and B or with Clostridium botulinum C3 exoenzyme for 48 hours attenuated the 5-HT-induced response but not the high K⁺-induced response. Application of the Rho-kinase inhibitor, Y-27632, resulted in marked inhibition of the 5-HT-induced response but had negligible effect on the high K⁺-induced response. These results suggest that the activation of Rho and Rho-kinase may be involved in the generation of the contraction produced by 5-HT in the bovine middle cerebral artery, while protein kinase C plays, if any, an insignificant role on the contraction.