The small G-protein RhoA and its down stream effector Rho-kinase (RhoK) have been proposed to be important players for mediating penile vasoconstriction. The aim of the present study was to evaluate the effects of RhoK inhibition on the calcium handling mechanisms elicited by a-1adrenoceptor activation in rat penile arteries, by using simultaneous measurements of intracellular Ca²⁺ [Ca^2+]i and force, as well as a-toxin-permeabilized arteries.

The a1-adrenoceptor agonist phenylephrine (Phe) increased both [Ca²⁺]i and tension, which were abolished by extracellular Ca²⁺ removal and reduced by about 50% by L-type voltage-dependent Ca²⁺ (VOC) channel blocker nifedipine. The RhoK inhibitor Y-27632 reduced the increase in both [Ca²⁺]i (49 ± 8 %) and tension (82 ± 3 %) induced by Phe. Sarcoplasmic reticulum depletion with cyclopiazonic acid (CPA) induced an increase in [Ca²⁺] (33 ± 2% of KPSS, n=4) not coupled to contraction. This capacitative calcium entry was reduced by 37 ± 5 % (n=4) by 2-APB, a store-operated Ca²⁺ (SOC) channel antagonist, but unaltered by Y-27632. In a-toxin-permeabilized penile arteries, activation of G-proteins with guanosine-5´-O-(3-thiophosphate) (GTP) and Phe both enhanced the myofilament sensitivity to Ca^2+. This Ca²⁺ sensitization was reduced by selective inhibitors of protein kinase C (PKC), tyrosine kinase (TK) and RhoK by 43%, 67% and 82%, respectively. The present data suggest the RhoK pathway is involved in both Ca2+ sensitization and in the regulation of Ca²⁺ entry through channels different from VOC or SOC channels in rat penile arteries. This work was supported by grant nordm; SAF2006-09191.