Contractile responses of the guinea-pig vas deferens to the combination of vanadium ions with ouabain.
1. Vanadate and vanadyl ions (10(-5)-10(-2) M) induced dose-dependent rhythmic contractions of the vas deferens of reserpine-treated guinea-pigs. The Na, K-ATPase blocker ouabain (10(-5)-10(-3) M) induced similar, though smaller, effects. Experiments were performed to verify if these effects are due to an interaction with the same receptor population. 2. Ouabain caused a striking potentiation of vanadium effects, which was also observed in denervated organs, indicating that a release of neuronal substances is not involved in potentiation. Similar potentiations were observed by combining vanadium with K-free solutions instead of ouabain, corroborating the involvement of the latter drug with Na, K, ATPase. 3. From the analysis of time-response and concentration-response curves, there are at least three indications that vanadium and ouabain interact with different sites: (a) the combined effect of both agonists was several times higher than the corresponding isolated effects; (b) the combined effect, expected to be independent of the order of addition of the agonist, was higher if vanadium was added before, than after ouabain; (c) the combined effect on the time elapsed between the addition of the two agonists, being higher if an interval of at least 10 min was allowed between vanadium and ouabain additions. 4. In conclusion, our results do not support the hypothesis that vanadium compounds and ouabain have a similar mechanism of action for the contraction induced in guinea-pig vas deferens.
Garcia
A G
AG
Department of Pharmacology, Escola Paulista de Medicina, São Paulo, Brazil.
Jurkiewicz
A
A
Jurkiewicz
N H
NH
D000818:Animals; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009121:Muscle Denervation; D009130:Muscle, Smooth / Q000187:drug effects*; D010042:Ouabain / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012110:Reserpine / Q000494:pharmacology; D014639:Vanadium / Q000494:pharmacology*; D015016:Yohimbine / Q000494:pharmacology
D014639:Vanadium; D015016:Yohimbine; D010042:Ouabain; D012110:Reserpine