Influences of sodium on the contractile action of vanadate in depolarized vas deferens and ureter of the guinea-pig.
Effects of extracellular Na+ on the contractile action of vanadate were studied using depolarized smooth muscles of the guinea-pig vas deferens and ureter. Both sodium vanadate and ammonium vanadate induced tension development of the preparations in K-Tyrode's solution containing 12.3 mM Na+. The tension developments were enhanced greatly in K-60 mM solution with 89.3 mM Na+ and diminished in Na+-free K-Tyrode's or Na+-free K-60 mM Tyrode's solution, and slight relaxations were observed in the vas deferens soaked in the latter two Na+-free solutions. The addition of Na+ to Na+-free solution in the presence of vanadate induced a marked increase in tension. Vanadate induced slight tension development of depolarized preparations in the absence of Ca which was less affected by Na+. Ca-induced contraction of depolarized preparations was also markedly potentiated by vanadate. The potentiation was more prominent in the presence of Na+ and less prominent in the absence of Na+; the maximum tension was less affected by Na+ than the vanadate-induced contraction of depolarized preparation, but the tension decay was greatly accelerated in the absence of Na+. It was suggested that Na+ enhances the contractile action of vanadate through Ca extrusion mechanism of cell membrane.
Research Institute of Hypertension, Kinki University, Osaka, Japan.
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Sunano
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Kato
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Moriyama
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Shimamura
D000818:Animals; D002118:Calcium / Q000502:physiology; D003106:Colon / Q000187:drug effects; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology*; D014513:Ureter / Q000187:drug effects; D014638:Vanadates / Q000494:pharmacology*; D014649:Vas Deferens / Q000187:drug effects
D014638:Vanadates; D012964:Sodium; D011188:Potassium; D002118:Calcium