Endothelin-1-induced vasospasms of spiral modiolar artery are mediated by Rho-kinase-induced Ca2+ sensitization of contractile apparatus and reversed by calcitonin gene-related peptide

Background and Purpose-Vasospasms of the spiral modiolar artery may cause an ischemic stroke of the inner ear that manifests itself by a sudden hearing loss. Previously we have shown that endothelin-1 (ET-1) induces vasospasms of the spiral modiolar artery. Here we tested the hypotheses that ET-1-induced vasospasms are (1) reversible by ETA receptor antagonists; (2) mediated by a Ca2+ sensitization of the contractile apparatus via a Rho-kinase-induced inhibition of myosin light chain phosphatase; and (3) reversible by the vasodilator calcitonin gene-related peptide (CGRP). Methods-The Ca2+ sensitivity of the contractile apparatus was evaluated by correlation between the smooth muscle, cell Ca2+ concentration and the vascular diameter, which were measured by microfluorometry with the fluorescent dye fluo-4 and videomicroscopy, respectively. Results-ET-1-induced vasospasms were prevented but not reversed by the ETA receptor antagonists BQ-123 and BMS-182874. The Ca2+ sensitivity of the contractile apparatus was increased by ET-1 and by inhibition of myosin light chain phosphatase with calyculin A and was decreased by CGRP. ET-1-induced vasospasms and Ca2+ sensitization were prevented and reversed by the Rho-kinase antagonist Y-27632 and by CGRP. Conclusions-ET-1 induces vasospasms of the spiral modiolar artery via ETA receptor-mediated activation of Rho-kinase, inhibition of myosin light chain phosphatase, and an increase in Ca2+ sensitivity, which is reversed by CGRP. The observation that vasospasms were reversed by Y-27632 but not by BQ-123 or BMS-182874 suggests that Rho-kinase, rather than the ETA receptor, is the most promising pharmacological target for the treatment of ET-1-induced vasospasms, ischemic strokes, and sudden hearing loss.