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

Abstract

1. The release of ATPase activity evoked by electrical field stimulation (EFS) (8 Hz, 25 s) was investigated in several tissues in which adenosine 5'-triphosphate (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 guinea-pig isolated urinary bladder contained ATPase activity. ATP breakdown was fastest in superfusate collected from the guinea-pig isolated vas deferens. However, EFS of the enteric nerves of the guinea-pig isolated taenia coli 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°C and 20°C. Lineweaver-Burke analysis of the initial rates of ATP hydrolysis gave a K(M) of 39 μM and a V(max) of 1039 pmol ATP metabolized min-1 ml-1 superfusate. 4. 6-N,N-diethyl-D-β,γ-dibromomethyleneATP (ARL 67156). pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) and pyridoxal-5'-phosphate (P-5-P) all inhibited the ATPase activity in a concentration-dependent manner 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 that are similar to ectonucleoside triphosphate diphosphohydrolases.