Abstract
Expression of two isoforms of Rho-kinase (ROCK) and its functional role in the physiological control of smooth muscle contraction in the sheep ureter were investigated. Helical strips of the ureteric smooth muscle were stimulated by electrical field stimulation (EFS, 60 V, 1 mS, 2, 4, 8, 16 and 32 Hz, for 20 S), KCl (80 mm), carbachol (CCh, 10(-8)-10(-4) m) or phenylephrine (Phe, 10(-8)-10(-4) m). EFS produced a reproducible contractile activity, which was abolished by tetrodotoxin (3 x 10(-6) m), a Na(+) channel blocker. A muscarinic receptor antagonist, atropine (2 x 10(-6) m), and an adrenergic neuron blocker, guanethidine (10(-5) m), significantly suppressed the contraction induced by EFS. However, this contraction was augmented in the presence of N(G)-nitro-l-arginine (l-NA, 10(-4) m), a nitric oxide synthase inhibitor. Two Rho-kinase inhibitors, Y-27632 (5 x 10(-5) m) and fasudil (5 x 10(-5) m), markedly attenuated the EFS-elicited contraction. CCh and Phe produced concentration-dependent contraction in the sheep ureter. pD(2) values for Phe and CCh were 5.04+/-0.11 and 5.00+/-0.22, respectively. Y-27632 (5 x 10(-5) m) and fasudil (5 x 10(-5) m) also significantly inhibited CCh- and Phe-induced contractions. Moreover, these ROCK inhibitors produced relaxations in the KCl-elicited contraction in a concentration-dependent manner. pD(2) values for Y-27632 and fasudil were, respectively, 5.17+/-0.07 and 4.58+/-0.08 (P<0.001). Furthermore, the influences of these agents were also tested on spontaneous phasic contractions of the tissue. Among Y-27632, fasudil, TTX, l-NA, guanethidine and atropine, only the ROCK inhibitors (10(-6)-10(-5) m) were able to suppress the spontaneous contractile activity. Western blot analysis has revealed that both isoforms of Rho-kinase (ROCK-1 and ROCK-2) are expressed in the sheep ureter. Densitometric analysis has indicated that these enzymes are less expressed in the sheep ureter than are in the sheep aorta in a significant manner. These results show that a contractile enzyme, Rho-kinase, is expressed, and it mediates agonist- and EFS-induced contractions as well as spontaneous contractile activity of the isolated sheep ureter. Since Y-27632 and fasudil depressed the contractions, it seems plausible to postulate that Rho-kinase inhibitors may be beneficial in the treatment of renal colic.