Tachyphylaxis to the inhibitory effect of manganese on potassium-induced contractions in the isolated vas deferens of the guinea pig.
In the isolated vas deferens of the guinea pig, the inhibitory effects of manganese (Mn2+) on the contractions induced by potassium (K+) were decreased when the contractions were induced repeatedly in the presence of Mn2+. This phenomenon appeared to be tachyphylaxis to the inhibitory effects of Mn2+. After the repetitive application of K+ with Mn2+, the phasic component of K(+)-induced contraction was restored, while the tonic component of this contraction and resting tone were augmented by the deprivation of extracellular Mn2+. When Mn2+ was applied during the tonic component of the K(+)-induced contraction, the phasic component of the next contraction induced by K+ in the absence of Mn2+ was slightly inhibited and the tonic component of the contraction was potentiated. When extracellular calcium concentration was increased, the inhibitory effect of Mn2+ on K(+)-induced contractions was reduced, while the tachyphylaxis to Mn2+ also appeared. Under this condition, the resting tone was markedly increased when the K(+)-induced contraction was repeated in the presence of Mn2+. In the calcium-free medium containing Mn2+, although K+ caused slow and monophasic contractions, the magnitude of the contractions was much smaller than that of the contractions induced in the normal medium containing Mn2+. These results suggest that the tachyphylaxis was not produced by the decrement of the inhibitory effects of Mn2+ on the contractions but by the augmenting effects of intracellularly accumulated Mn2+ and that these augmenting effects of Mn2+ are not due to the direct action on the contractile proteins but due to the indirect action of Mn2+ which increased the availability of Ca2+.
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Kanazawa University, Japan.
H
H
Ushijima
Y
Y
Gomi
D000818:Animals; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008345:Manganese / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009129:Muscle Tonus / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology*; D013618:Tachyphylaxis / Q000502:physiology*; D014649:Vas Deferens / Q000187:drug effects
D008345:Manganese; D011188:Potassium