Effects of P-2-purinoceptor antagonists on ecto-nucleotidase activity of guinea-pig vas deferens cultured smooth muscle cells

Ecto-nucleotidase activity was studied on primary cultures of guinea-pig vas deferens smooth muscle cells by measuring the inorganic phosphate (P-i) production using ATP as a substrate. The ecto-nucleotidase was insensitive to ouabain, oligomycin, sodium azide, p-nitrophenyl phosphate and beta-glycerophosphate. Enzyme activity was highly dependent on either Ca2+ or Mg2+. Antagonists of P-2X-purinoceptors, pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid, 4,4'-diisothiocyanatostilbene-2,2'-disulphon suramin and pyridoxal-5-phosphate, significantly inhibited ecto-nucleotidase activity. In contrast, the P-1-purinoceptor antagonists, 8-p-sulphophenyl theophylline and 1,3-dipropyl-8-cyclopentyl-xanthine, did not affect the enzyme activity. Thus, when P-2-purinoceptors are studied by testing agonists and antagonists potencies, the inhibition of ecto-nucleotidase activity by currently available P-2-purinoceptor antagonists should be taken into account.