Modulation of voltage-gated Ca(2+) channel current (I(Ca)) regulates secretion of catecholamines from adrenal chromaffin cells. Previous work demonstrated that I(Ca) can be augmented by phosphorylation to increase secretion or that inhibition of I(Ca) results in diminished catecholamine secretion. In the current manuscript, we show that stimulation of chromaffin cells results in the release of an "endogenous inhibitor" that suppresses I(Ca). The inhibition is due to the secretion of ATP, which is stored at high concentrations in secretory granules and is coreleased with catecholamines upon stimulation. The ATP exerts its actions through P(2 gamma) purinoceptors and inhibits both N- and P/Q-type Ca (2+) channels in a voltage-dependent manner but with different efficacies. Overall, we have identified and characterized a negative feedback pathway that may serve as an important regulatory mechanism for catecholamine secretion in chromaffin cells.