Inhibition of rat parotid ecto-ATPase activity

The inhibitory profile of several known and suspected ecto-ATPase inhibitor s was compared on ecto-ATPase activity in rat parotid plasma membranes. Tho se chemicals with high IC50 (above 130 mu M) were the nucleotides alpha,bet a-methylene ATP, beta,gamma-methylene ATP, 2-methylthio ATP, inosine tripho sphate. 5'-p-fluorosulphonylbenzoyladenosine, the sulphonates, 1-amino-2-na phthol-4-sulphonic acid, Coomassie brilliant blue G. and the stilbene disul phonates, DIDS and SITS. Those agents with low IC50 were: Coomassie brillia nt 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 inhi bitors of ATP hydrolysis by whole parotid acinar cells. ARL67156, a selecti ve inhibitor of ecto-ATPase, had an IC50 of approx. 120 mu M. Suramin displ ayed non-competitive inhibition of ecto-ATPase whereas the inhibitory effec ts of ATP gamma S and Reactive blue 2 were curvilinear on Dixon plots. Thes e results define the effects of various agents on ecto-ATPase in an exocrin e tissue that has been shown to respond to extracellular ATP. (C) 1999 Else vier Science Ltd. All rights reserved.