title: The involvement of fast calcium channel activity in the selective activation of phasic contractions by partial depolarization in rat vas deferens smooth muscle.
abstract: In the prostatic portion of the rat vas deferens, 65% of the preparations studied developed pronounced rapid twitch activity in response to slight depolarization by 15 mM K+ salines. The mechanism underlying this response was studied using treatments designed to inhibit the influence of endogenous transmitters and using recognized calcium antagonist drugs. Although the action of phentolamine was inconclusive, experiments employing guanethidine, reserpine, 6-hydroxydopamine, atropine and alpha,beta-methylene ATP suggest that endogenous transmitter release was not responsible for the observed twitch activity. Twitch activity was strongly dependent upon [Ca]0. The 15 mM K+ twitch activity was inhibited by verapamil (5 X 10(-5) M) but was resistant to 10(-3) M lanthanum. Twitch activity was, however, abolished by 10(-3) M Mn2+ ions and was markedly potentiated by 2 X 10(-3) M TEA. The rapid twitch activity exhibited a strong voltage-dependency, being abolished by [K]0 elevations of 25 mM and above. It is concluded that this phasic activity of the vas deferens smooth muscle may depend upon fast calcium channel activity which, in contrast to voltage-dependent slow calcium channel activity, shows ready voltage-inactivation on substantial depolarization.
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D014649:Vas Deferens / Q000187:drug effects
chemical_list: D007473:Ion Channels; D011188:Potassium; D002118:Calcium