부산대학교 도서관

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.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.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 KMof 39 μMand a Vmaxof 1039 pmol ATP metabolized min−1ml−1superfusate.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.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.