Abstract
The effects of sodium vanadate on electrical and mechanical activities of the guinea-pig ureter were studied. Sodium vanadate at concentrations higher than 10(-5) M induced elevations of basal tension and repetitive twitch-like contractions. The drug depolarized membrane only slightly but induced repetitive action potentials. Sodium vanadate potentiated phasic and tonic contractions of K-contracture. It also increased tension development of high amplitude in K-depolarized preparations. Thus, the change in the resting membrane potential does not seem to play the only role in the initiation of contractions, though sodium vanadate-induced twitch-like contractions were associated by repetitive action potentials. Sodium vanadate-induced twitch-like contractions were blocked by Ca removal or by verapamil, but elevated basal tension was depressed only slightly under these treatments. Sodium vanadate induced tension development in the absence of Ca both in polarized and K-depolarized preparations. These results suggest that sodium vanadate increased mechanical activities by enhancing Ca influx as well as releasing intracellular bound Ca and/or inhibiting Ca extrusion through cell membrane.
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