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Effects of cyclopiazonic acid on rhythmic contractions in uterine smooth muscle bundles of the rat
Author(s) -
Kasai Yasuyo,
Iino Masamitsu,
Tsutsumi Osamu,
Taketani Yuji,
Endo Makoto
Publication year - 1994
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1994.tb13201.x
Subject(s) - cyclopiazonic acid , oxytocin , medicine , endocrinology , contraction (grammar) , intracellular , inhibitory postsynaptic potential , muscle contraction , chemistry , depolarization , biophysics , biology , biochemistry
1 We studied the effects of cyclopiazonic acid (CPA) on rhythmic contractions and on Ca 2+ uptake by the intracellular stores in longitudinal muscle strips of the rat uterus at 30°C. 2 Oxytocin (1 μ m ) in Ca 2+ ‐free solution induced a transient rise in the intracellular Ca 2+ concentration ([Ca 2+ ] i ) and contraction after Ca 2+ loading of the stores in high‐K + ‐ and Ca 2+ ‐containing solution. CPA inhibited oxytocin‐induced Ca 2+ release and contraction, the half and full inhibitory concentrations of CPA being 0.3 and 10 μ m , respectively. In contrast, addition of CPA after Ca 2+ loading exerted no significant inhibitory effects. 3 Oxytocin (10 nM) applied in Ca 2+ ‐containing solution induced rhythmic increases in both force and [Ca 2+ ] i . CPA (10 μ m ) had no effect on oxytocin‐induced rhythmic contractions. 4 At a high concentration (300 μ m ), CPA inhibited the rhythmic contractions induced by 10 nM oxytocin; the frequency and the peak height were decreased, and in many bundles contractions were completely abolished. These inhibitory effects were reversed after CPA washout. 5 CPA (300 μ m ) inhibited the rate of rise of [Ca 2+ ] i due to depolarization induced by high‐K + ‐containing solution. 6 These results suggest that low concentrations of CPA inhibit the loading of Ca 2+ into intracellular stores in intact tissue strips, and that the Ca 2+ stores are not directly involved in the uterine rhythmic contractions. It is also suggested that a high concentration of CPA inhibits the mechanism that is responsible for the generation of rhythmic contractions as well as voltage‐dependent Ca 2+ channels.