Effects of vanadate on mechanical and electrical activities in guinea-pig taenia coli

Effects of vanadate (NH4VO3 and Na3 VO4: VAN) on electrical and mechanical activities and cellular Na content in guinea-pig taenia coli were examined. VAN (1-5 X 10(-4) M) transiently increased membrane potential and decreased muscle tension. Several minutes later, muscle tension increased following membrane depolarization and increase in spike frequency. The initial relaxing effect of VAN was not affected by ouabain, phentolamine and propranolol, and the contractile effect was not affected by atropine and tetrodotoxin. The VAN-induced contraction was dependent on external Ca and was abolished by verapamil. VAN also induced a contraction in depolarized taenia, which was augmented when external Ca concentration was lowered. VAN (10(-3) M) did not change cellular Na content. It is suggested that VAN-induced relaxation is due to the decrease in membrane electrical activities whereas contraction is attributable to the increased electrical activities followed by Ca influx and also to nonelectrical mechanism followed by mobilization of cellular Ca. These changes do not seem to be related to Na pump activity.