Selective and competitive antagonism by suramin of ATP‐stimulated catecholamine‐secretion from PC12 phaeochromocytoma cells

1 Suramin, a putative P2‐antagonist, (10 to 300 μm) inhibited the adenosine 5′‐triphosphate (ATP)‐stimulated secretion of [3H]‐noradrenaline or endogenous dopamine from phaeochromocytoma PC12 cells in a concentration‐dependent manner. Suramin (300 μm) 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.