Modulation of calcium current by ATP in guinea-pig adrenal chromaffin cells

The effects of extracellular adenosine 5-triphosphate (ATP) on voltage-dependent Ca²⁺ currents were examined using the whole-cell voltage-clamp technique in guinea-pig isolated adrenal chromaffin cells. ATP (500 M) reversibly suppressed Ca²⁺ currents in the presence of 5 mM Ca²⁺ in the extracellular solution. The inhibitory effect of ATP on Ca²⁺ currents tended to increase with increases in the peak amplitude of ATP-evoked current when the intracellular solution contained 0.1 or 1 mM ethylenebis(oxonitrilo)tetraacetate(EGTA). Using the intracellular solution containing 10 mM EGTA, on the other hand, the inhibitory efftect did not change regardless of the amplitude of current responses to ATP In the presence of 10 mM Ba²⁺, ATP (100 mol/l). reduced Ba²⁺ currents in a manner similar to Ca²⁺ currents. This reduction was decreased by dialysis of cells with the internal solution containing guanosine 5-O-(2-thiodiphosphate) (GDP -S]; 1 mM) or guanosine 5-O-(3-thiotriphos-phate) (GTP -S]; 100 mol/l). A depolarizing prepulse channels. In addition, ATP seems to modulate Ca²⁺ channels via the pathway related to G-protein. Adenine nucleotides and adenosine may play a role in controlling secretory activity in guinea-pig adrenal chromaffin cells.