Cholinergic potentiation by ouabain in the contraction of guinea-pig vas deferens through pre- and post-synaptic mechanism.
In the guinea-pig vas deferens, the contractions induced by pilocarpine and arecoline, unlike ACh, were markedly reduced by treatment with procaine (10(-6) g/ml) or hemicholinium (5 x 10(-4) g/ml). These reductions by hemicholinium were completely recovered after exposure to choline. The contractile responses to these three agonists were eliminated by atropine (3 x 10(-8) g/ml) but enhanced by neostigmine (3 x 10(-8) g/ml), though these were not affected at all by tetrodotoxin (3 x 10(-8) g/ml) or hexamethonium (10(-5) g/ml). The contractile responses to ACh, pilocarpine and arecoline were potentiated by ouabain (10(-6) g/ml). These potentiations were more marked in pilocarpine and arecoline than those in ACh. The potentiation in response to arecoline was maximal after incubation with ouabain for 5 min but that to ACh for 45 min. The results suggest that pilocarpine and arecoline act as ACh-releaser in this tissue and that the ouabain-induced cholinergic potentiation may be attributable to a dual mechanism, facilitation of ACh release at presynaptic site and alteration of the membrane excitability at postsynaptic site.
D000818:Animals; D001115:Arecoline / Q000494:pharmacology; D004347:Drug Interactions; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D010042:Ouabain / Q000494:pharmacology*; D010275:Parasympathetic Nervous System / Q000187:drug effects*; D010277:Parasympathomimetics / Q000494:pharmacology; D010862:Pilocarpine / Q000494:pharmacology; D013997:Time Factors; D014649:Vas Deferens / Q000187:drug effects
D010277:Parasympathomimetics; D010862:Pilocarpine; D001115:Arecoline; D010042:Ouabain