Rho-dependent kinase is involved in agonist-activated calcium entry in rat arteries

The present study was aimed at investigating whether, besides its pivotal role in Ca(2+)-independent contraction of smooth muscle, Rho-kinase is involved in the mechanisms underlying the Ca2+ signal activated by noradrenaline in arteries. In rat aorta and mesenteric artery, the Rho-kinase inhibitor Y-27632 (10 microM) completely relaxed the contraction evoked by noradrenaline (1 microM) and simultaneously inhibited the Ca2+ signal by 54 +/- 1 % (mesenteric artery) and 71 +/- 15 % (aorta), and the cell membrane depolarisation by 56 +/- 11 % (mesenteric artery). A similar effect was observed in arteries contracted by AlF4-, while in KCl-contracted arteries, Y-27632 decreased tension without changing cytosolic Ca2+. The same effects were observed with another inhibitor of Rho-kinase (HA1077) but not with an inhibitor of protein kinase C (Ro-31-8220). Effects of Y-27632 were not prevented by incubating the artery in 25 mM KCl, with K+ channel blockers or with the Ca2+ channel blocker nimodipine. Y-27632 did not affect either the increase in the production of inositol phosphates activated by noradrenaline, or the release of Ca2+ from non-mitochondrial stores evoked by InsP3 in permeabilised aortic cells, or the Ca2+ signals evoked by thapsigargin or caffeine. The capacitative Ca2+ entry activated by thapsigargin was not impaired by Y-27632, but the entry of Ba2+ activated by noradrenaline in the presence of nimodipine was blocked by 10 microM Y-27632. These results indicate that Rho-kinase is involved in noradrenaline activation of a Ca2+ entry distinct from voltage- or store-operated channels in rat arteries.