SELECTIVE AND COMPETITIVE ANTAGONISM BY SURAMIN OF ATP-STIMULATED CATECHOLAMINE-SECRETION FROM PC12 PHEOCHROMOCYTOMA CELLS

1 Suramin, a putative P2-antagonist, (10 to 300-mu-M) inhibited the adenosine 5'-triphosphate (ATP)-stimulated secretion of [H-3]-noradrenaline or endogenous dopamine from phaeochromocytoma PC12 cells in a concentration-dependent manner. Suramin (300-mu-M) did not affect the dopamine-secretion stimulated by high K+ or nicotine. 2 Suramin shifted the concentration-response curve for ATP to the right. The antagonism was competitive with a pA2 value of 4.52. 3 ATP also stimulated an increase in intracellular Ca2+ concentration as determined by fura-2 methods. Suramin antagonized this effect over the same concentration range that antagonized the ATP-stimulated catecholamine secretion. 4 These results suggest that suramin can be used as a selective and competitive antagonist of ATP in experiments concerning mechanisms of catecholamine-secretion.