Effects of K(+)-free solution of contractile responses of rat vas deferens

The effect of K(+)-free solution as well as its modulatory effect on neurogenic and agonist-induced contractile responses in rat vas deferens were investigated in the present study. Isolated rat vas deferens, normally a quiescent smooth muscle, developed spontaneous contractions on exposure to K(+)-free solution which was not affected by tetrodotoxin (3 x 10(-7) mol/l) or prazosin (10(-6) mol/l) but was abolished in Ca(2+)-free medium. Transmural field stimulus (3-30 Hz; 0.5 ms duration; supramaximal voltage; 10 s) induced biphasic responses, consisting of fast and slow components, were markedly inhibited in K(+)-free medium and were restored on readdition of K+ to the medium. Similarly, the twitch responses at 0.1 Hz were also inhibited in K(+)-free solution. In the absence of K+, the sensitivity of the tissues to noradrenaline (10(-6) to 10(-4) mol/l) and ATP (10(-4) mol/l) was not significantly altered. The observations made in the present study suggest that spontaneous contractions induced by K(+)-free solution are myogenic in origin and are dependent on extracellular Ca2+. Selective inhibition of neurogenic responses in K(+)-free medium without any significant effect on exogenous noradrenaline and ATP is suggestive of the involvement of prejunctional inhibition of neurotransmitter release.