Inhibition of rat parotid ecto-ATPase activity

The inhibitory profile of several known and suspected ecto-ATPase inhibitors was compared on ecto-ATPase activity in rat parotid plasma membranes. Those chemicals with high IC50 (above 130 mu M) were the nucleotides alpha,beta-methylene ATP, beta,gamma-methylene ATP, 2-methylthio ATP, inosine triphosphate. 5'-p-fluorosulphonylbenzoyladenosine, the sulphonates, 1-amino-2-naphthol-4-sulphonic acid, Coomassie brilliant blue G. and the stilbene disulphonates, DIDS and SITS. Those agents with low IC50 were: Coomassie brilliant blue R (114 mu M), ATP gamma S (49 mu M), suramin (72 mu M) and Reactive blue 2 (25 mu M). The last three inhibitors have similar potencies as inhibitors of ATP hydrolysis by whole parotid acinar cells. ARL67156, a selective inhibitor of ecto-ATPase, had an IC50 of approx. 120 mu M. Suramin displayed non-competitive inhibition of ecto-ATPase whereas the inhibitory effects of ATP gamma S and Reactive blue 2 were curvilinear on Dixon plots. These results define the effects of various agents on ecto-ATPase in an exocrine tissue that has been shown to respond to extracellular ATP. (C) 1999 Elsevier Science Ltd. All rights reserved.