Effects of vanadate on mechanical responses and Na-K pump in vascular smooth muscle |
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Authors: | Hiroshi Ozaki Norimoto Urakawa |
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Affiliation: | Department of Veterinary Pharmacology, Faculty of Agriculture, University of Tokyo, Bunkyo-ku, Tokyo, 113, Japan |
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Abstract: | The effects of vanadate on tension and on the Na-K pump in isolated guinea-pig aorta were investigated. Vanadates (NH4VO3 or Na3VO4 · nH2O) (10?3 M) produced a sustained contraction (about 0.5 g) which was not influenced by phentolamine (10?6 M). In the absence of external Ca, vanadate and norepinephrine (2 × 10?6 M) induced a small contraction, although high K (45.4 mM) did not. In a Ca-depleted, high K (142.2 mM) solution, vanadate and norepinephrine still caused muscle contraction. D600 (10?6 M) slightly inhibited the contractions induced by vanadate and norepinephrine, while this agent completely inhibited the contraction induced by high K. Sodium nitroprusside (10?5 M) strongly inhibited the contractions induced by vanadate and norepinephrine but not the contraction induced by high K. Vanadate produced a contraction in K-free solution with ouabain (10?4 M). The tissue K content did not change during a 2 h treatment of the muscle with vanadate. Reaccumulation of K following a 3 h treatment of the muscle with K-free solution was inhibited by ouabain but not by vanadate. These results indicate a similarity between the contractions induced by vanadate and by norepinephrine and suggest that the vanadate-induced contraction is not due to an inhibition of the Na-K pump. |
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Keywords: | Vanadate Vascular smooth muscle Norepinephrine Na-K pump High K |
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