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Propylbenzilylcholine Mustard(PrBCM)-Sensitive Cholinoceptors and Contractile Response to Partial Agonist in Guinea Pig Ileal Muscle.
Author(s) -
Issei Takayanagi,
Hiroshi Ohtsuki,
Kanji Saito,
Kenichi Koike,
Mitsutoshi Satoh
Publication year - 1991
Publication title -
japanese journal of pharmacology/japanese journal of pharmacology
Language(s) - English
Resource type - Journals
eISSN - 1347-3506
pISSN - 0021-5198
DOI - 10.1254/jjp.56.151
Subject(s) - carbachol , phenoxybenzamine , pilocarpine , medicine , endocrinology , agonist , chemistry , guinea pig , receptor , biology , neuroscience , epilepsy
Pilocarpine, a partial agonist, activates propylbenzilylcholine mustard (PrBCM)-sensitive cholinoceptors in the guinea pig ileal longitudinal muscle, while carbachol, a full agonist, predominantly activates PrBCM-resistant ones. Carbachol behaves as a partial agonist in the preparation treated with phenoxybenzamine and mainly activates PrBCM-sensitive cholinoceptors, as phenoxybenzamine preferably blocks PrBCM-resistant ones. The receptor occupancy-response curve for carbachol became a rectangular hyperbola, while pilocarpine showed a linear relation. After occlusion of cholinoceptors with phenoxybenzamine, carbachol showed a linear receptor occupancy-response relation, suggesting that its contraction mechanisms after occlusion of cholinoceptors resemble those for pilocarpine. Both the agonists induced an increase in cytosolic Ca2+ concentration [( Ca2+]i) and tension development in a concentration-dependent manner under the conditions used herein. The slopes of the regression lines between [Ca2+]i and tension development for pilocarpine in the untreated preparation and for carbachol in the preparation treated with phenoxybenzamine were significantly steeper than that for carbachol in the untreated preparation, suggesting that carbachol in the phenoxybenzamine-treated preparation and pilocarpine induced a greater tension for a given increase in low [Ca2+]i than did carbachol. Thus an activation of PrBCM-sensitive cholinoceptors might enhance the Ca2+-sensitivity of the contractile elements.

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