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.