Involvement of Ca2+ sensitization in ropivacaine-induced contraction of rat aortic smooth muscle.

BACKGROUND The mechanisms of amino-amide local anesthetic agent-induced vasoconstriction remain unclear. The current study was designed to examine the roles of the protein kinase C (PKC), Rho kinase, and p44/42 mitogen-activated protein kinase (p44/42 MAPK) signaling pathways in calcium (Ca2+)-sensitization mechanisms in ropivacaine-induced vascular contraction. METHODS Endothelium-denuded rat aortic rings, segments, and strips were prepared. The cumulative dose-response relations of contraction and intracellular Ca2+ concentration to ropivacaine were tested, using isometric force transducers and a fluorometer, respectively. The dose-dependent ropivacaine-induced phosphorylation of PKC and p44/42 MAPK and the membrane translocation of Rho kinase were also detected using Western blotting. RESULTS Ropivacaine induced a dose-dependent biphasic contractile response and an increase in intracellular Ca2+ concentration of rat aortic rings, increasing at concentrations of 3 x 10 m to 3 x 10 m and decreasing from 10 m to 3 x 10 m, with a greater tension/intracellular Ca2+ concentration ratio than that induced with potassium chloride. The contraction was attenuated in a dose-dependent manner, by the PKC inhibitors bisindolylmaleimide I and calphostin C, the Rho-kinase inhibitor Y 27632, and the p44/42 MAPK inhibitor PD 098059. Ropivacaine also induced an increase in phosphorylation of PKC and p44/42 MAPK, and membrane translocation of Rho kinase in accordance with the contractile responses, which were also significantly inhibited by bisindolylmaleimide I and calphostin C, Y 27632, and PD 098059, correspondingly. CONCLUSION These findings demonstrated that PKC-, Rho kinase-, and p44/42 MAPK-mediated Ca2+-sensitization mechanisms are involved in the ropivacaine-induced biphasic contraction of rat aortic smooth muscle.