Greater Contraction Is Induced by Pilocarpine than by Carbachol at the Same Levels of Cytosolic Ca²⁺ Concentration in Isolated Longitudinal Muscle of Guinea Pig Ileum

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Pilocarpine, which activates propylbenzilylcholine mustard (PrBCM)-sensitive cholinoceptors, and carbachol, which activates PrBCM-resistant ones, induced an increase in cytosolic Ca²⁺ concentration ([Ca²⁺]_i) and tension development in a concentration dependent manner in isolated longitudinal muscle of guinea pig ileum. A positive correlation between [Ca²⁺]_i and tension development due to both of the agonists was noted. The slope of regression line between two values for pilocarpine was steeper than that for carbachol, suggesting that pilocarine induced greater tension for a given increase in [Ca²⁺]_i than did carbachol. Thus an activation of PrBCM-sensitive cholinoceptors might enhance the Ca²⁺-sensitivity of the contractile elements.