Effect of apamin and theophylline on adenosine-5'-triphosphate-induced response of the guinea pig gallbladder.

Adenosine-5'-triphosphate (ATP) produced the rapid relaxation followed by the contraction in the gallbladder strips from guinea pig. The contractile response to ATP was antagonized with theophylline, but not with apamin and atropine. The dose-response curve for ATP-induced contraction was shifted to the right by theophylline. The relaxation induced by ATP was blocked by apamin, but not by theophylline, phentolamine and propranolol. The dose-response curve for ATP-induced relaxation was shifted to the right and downwards by apamin. These results indicate that two kinds of receptors for ATP exist in the guinea pig gallbladder and the theophylline-sensitive receptors may be involved in the contractile response and the apamin-sensitive receptors in relaxation.