title: Mechanism of tachyphylaxis on the inhibitory effect of manganese on agonist-induced contractions in the isolated vas deferens of the guinea pig.
abstract: In the isolated vas deferens of the guinea pig, the inhibitory effect of manganese (Mn2+) on contractions induced by norepinephrine decreased when the contractions were induced repeatedly in the presence of Mn2+. This phenomenon, "tachyphylaxis" to the inhibitory effect of Mn2+, was minimally observed when contractions were induced by acetylcholine. Contractions induced by acetylcholine as well as by norepinephrine in a Mn(2+)-free medium were augmented in preparations in which manganese had accumulated intracellularly by repetitive applications of high potassium in the presence of Mn2+. The magnitudes of their augmentation were dependent on the manganese contents of the preparations. The augmented contractions were remarkably resistant to the inhibitory effect of Mn2+ applied to the medium. These results suggest that intracellular manganese augments the contractions and this augmentation results in an apparent decrease in the inhibitory effect of Mn2+ in the medium.
authors.affiliation: Department of Pharmacology, Faculty of Pharmaceutical Sciences, Kanazawa University, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Tsunobuchi-Ushijima
authors.forename: Y
authors.initials: Y
authors.lastname: Gomi
mesh_terms: D000109:Acetylcholine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008345:Manganese / Q000378:metabolism / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009638:Norepinephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D013618:Tachyphylaxis / Q000502:physiology*; D014649:Vas Deferens / Q000187:drug effects* / Q000502:physiology
chemical_list: D008345:Manganese; D000109:Acetylcholine; D009638:Norepinephrine