Effects of suramin and PPADS on contractions evoked by ATP. The effects of (a) suramin and (b) PPADS on contractions of rat isolated SPA induced by ATP are shown. Cumulative concentration-response curves to ATP (10-7 - 3 × 10-4 M) were obtained in rings in the absence of antagonist (control) or in the presence of 3 × 10-5, 10-4 or 3 × 10-4 M of antagonist. Contractions are expressed as a percentage of the contraction induced by 4 × 10-2 M KCl. Vertical lines show s.e.mean. n = 5 for suramin and 4 for PPADS.