Mechanism of Tachyphylaxis on the Inhibitory Effect of Manganese on Agonist-Induced Contractions in the Isolated Vas Deferens of the Guinea Pig

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In the isolated vas deferens of the guinea pig, the inhibitory effect of manganese (Mn^<2+>) on contractions induced by norepinephrine decreased when the contractions were induced repeatedly in the presence of Mn^<2+>. This phenomenon, "tachyphylaxis" to the inhibitory effect of Mn^<2+>, 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 Mn^<2+>. 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 Mn^<2+> 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 Mn^<2+> in the medium.
公益社団法人日本薬学会の論文
1995-02-15