Adenosine 5'-triphosphate release evoked by electrical nerve stimulation from the guinea-pig gallbladder

The endogenous release of adenosine 5'-triphosphate (ATP) from strips of guinea-pig gallbladder during transmural stimulation (TS) was measured with a firefly luciferine-luciferase reaction. TS (15V, 1 ms, 0.5-5 Hz, for 1 min) caused a rapid and marked increase of ATP release in a frequency-dependent manner. Both ATP release and contractions evoked by TS (15 V, 5 Hz, 1 ms) were completely abolished in Ca-free medium. BaCl2 (3 X 10(-3) M), a direct muscle stimulant, produced almost the same degree of contractile tension as TS (15 V, 5 Hz, 1 ms) while the ATP release induced by BaCl2 was significantly reduced to about 60 percent of that induced by TS. Atropine (10(-6) M) significantly reduced TS-evoked contraction without affecting ATP release. It was suggested, therefore, that some of the ATP release induced by TS was of neural origin. Theophylline (a P1-purinoreceptor antagonist) 10(-6) M, quinidine (a non-specific P2-purinoreceptor antagonist) 10(-6) M and apamin (a potassium channel blocking agent) 10(-8) M had no effects on TS-evoked contraction and ATP release, suggesting the absence of a presynaptic autoregulatory mechanism of ATP release in the guinea-pig gallbladder.