Characteristics of ATP-induced catecholamine secretion from adrenal chromaffin cells of the guinea-pig

The effect of ATP on catecholamine secretion and intracellular Ca2+ concentration ([Ca2+](i)) was examined using perfused adrenal glands and dispersed chromaffin cells of the guinea-pig. The application of ATP (2 to 10 mM) for 2 min caused a dose-dependent increase in catecholamine secretion from perfused adrenal glands. ADP, but neither AMP nor adenosine, was also effective in increasing catecholamine secretion, though its potency was much less than that of ATP. 3. The ATP-induced secretory response was observed even under Na+-deficient conditions, but was reversibly abolished by removal of extracellular Ca2+. 4. In dispersed chromaffin cells, ATP (0.5 mM) caused increases in catecholamine secretion and [Ca2+](i), both of which were abolished after the removal of extracellular Ca2+, 5. These results indicate that ATP released from adrenal chromaffin cells together with catecholamine may exert a positive feedback influence on the following exocytotic catecholamine secretion. This effect may be accomplished by increasing the entry of extracellular Ca2+, but not by mobilizing intracellular Ca2+ stores in adrenal chromaffin cells of the guinea-pig.