Characterization of the ATPase released during sympathetic nerve stimulation of the guinea-pig isolated vas deferens

1 The release of ATPase activity evoked by electrical field stimulation (EF S) (8 Hz, 75 s) was investigated in several tissues in which adenosine 5'-t riphosphate (ATP) acts as a neurotransmitter. 2 Superfusate collected during EFS of sympathetic nerves of the guinea-pig, rat and mouse isolated vas deferens and parasympathetic nerves of the guin ea-pig isolated urinary bladder contained ATPase activity. ATP breakdown wa s fastest in superfusate collected from the guinea-pig isolated vas deferen s. However, EFS of the enteric nerves of the guinea-pig isolated taenia col i did not release any detectable ATPase. 3 The ATPase released from the guinea-pig isolated vas deferens metabolized ATP at similar rates at incubation temperatures of 37 degrees C and 20 deg rees C. Lineweaver-Burke analysis of the initial rates of ATP hydrolysis ga ve a K-M of 39 mu M and a V-max of 1039 pmol ATP metabolized min(-1) ml(-1) superfusate. 4 6-N,N-diethyl-D-beta,gamma-dibromomethyleneATP (ARL 67156), pyridoxalphos phate-6-azophenyl-2',4'-disulphonic acid (PPADS) and pyridoxal-5'-phosphate (P-5-P) all inhibited the ATPase activity in a concentration-dependent man ner with a potency order of ARL 67156 = PPADS > P-5-P. 5 In conclusion, EFS of several tissues in which ATP is a neurotransmitter causes the release of an ATPase and activity is greatest in the guinea-pig vas deferens. The enzyme has pharmacological and kinetic characteristics th at are similar to ectonucleoside triphosphate diphosphohydrolases.