Rho kinase is involved in Ca~(2+) entry of rat penile small arteries

摘要

Tonic physiological activity of RhoA/Rho kinase contributes to the maintenance of penile flaccidity through its involvement in the Ca~(2+) sensitization of erectile tissue smooth muscle. The present study hypothesized that Rho kinase is also involved in the modulation of Ca~(2+) entry induced by alpha_1-adrenoceptor stimulation of penile arteries. Rat penile arteries were mounted in microvascular myographs for simultaneous measurements of intracellular Ca~(2+) ([Ca~(2+)]_i) and force. The Rho-kinase inhibitor Y-27632 markedly reduced norepinephrine-mediated electrically induced contractions and the increases in both [Ca~(2+)]_i and tension elicited by the alpha_1-adrenoceptor agonist phenylephrine (Phe). In contrast, the protein kinase C (PKC) inhibitor Ro-31-8220 reduced tension without altering the Phe-induced increase in [Ca~(2+)]_i. In the presence of nifedipine, Y-27632 still inhibited the non-L-type Ca~(2+) signal and blunted Phe contraction. Y-27632 did not impair the capacitative Ca~(2+) entry evoked by store depletion with cyclopiazonic acid but largely reduced the Ba~(2+) influx stimulated by Phe in fura-2 AM-loaded arteries. The addition of Y-27632 to arteries depolarized with high KCl markedly reduced tension without changing [Ca~(2+)]_i. In alpha-toxin-permeabilized penile arteries stimulated with threshold Ca~(2+) concentrations, Y-27632 inhibited the sensitization induced by either guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) or Phe in the presence of GTPgammaS. However, Y-27632 failed to alter contractions induced by a maximal concentration of free Ca~(2+). These results suggest that Rho kinase, besides its contribution to the Ca~(2+) sensitization of the contractile proteins, is also involved in the regulation of Ca~(2+) entry through a nonselective cation channel activated by alpha_1-adenoceptor stimulation in rat penile arteries.