Effect of tris buffer on the contractile responses of rat vas deferens
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The influences of Tris-(hydroxymethyl)aminomethane (Tris) on the contractile responses of rat vas deferens to norepinephrine (NE), potassium chloride (KCl) and field stimulation were investigated. Equilibration of rat vas deferens muscle strips in Tris containing Tyrode medium caused a significant increase in sensitivity to KCl, but had no effect on the maximum tension induced by NE or KCl. The biphasic responses to 10(-4) M NE and 100 mM KCl, characterized by an initial fast (F) component followed by a slow (S) component, were differentially affected by Tris. The F components of NE- or KCl-induced contractions were significantly potentiated by Tris, whereas the S components of NE- or KCl-induced contractions were depressed. When the muscle strips were washed after NE- or KCl-induced contraction, the rate of relaxation reflecting the rate of loss of the sustained S-component was significantly slower in Tris-Tyrode than in Tyrode medium. In Ca2+ free medium, the F component of NE-induced contraction but not the S component was markedly potentiated by Tris. Verapamil (10(-5) M) eliminated the potentiation by Tris of the F component and further reduced the S component of the NE-induced contraction in the Tris-Tyrode medium. Both F and S components of KCl-induced contractions of rat vas deferens were sensitive to verapamil and these depressant effects were further enhanced in the presence of Tris. The contraction elicited by field stimulation was also biphasic. However, only the S component was significantly depressed by Tris and this inhibitory effect was irreversible. We conclude that Tris can exert adverse effects on the contractile properties of rat vas deferens, probably via the disturbance of Ca2+-handling by the smooth muscle membrane and possibly by affecting release of norepinephrine.
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