Mechanisms underlying facilitation by dopamine of ATP-activated currents in rat pheochromocytoma cells.

Mechanisms underlying facilitation by dopamine of extracellular adenosine 5'-triphosphate (ATP)-activated current were investigated in rat pheochromocytoma PC12 cells using the whole-cell voltage-clamp techniques. Dopamine (10 and 100 microM) augmented the peak amplitude of an inward current elicited by ATP (3-100 microM). The activation time course of the ATP-evoked current was accelerated by dopamine; the presence of 10 microM dopamine shifted the dependence of activation rate constants on the concentration of ATP toward a lower concentration range two fold. Dopamine also accelerated the inactivation and the deactivation, which was determined from the current decay upon washout of ATP. Intracellular mediators responsible for the dopamine-induced facilitation was estimated by loading various compounds in patch pipettes. Facilitation was not observed when K-252a (1 microM), a protein kinase inhibitor, was included in the intracellular solution. In addition, facilitation was also attenuated by intracellular adenosine 5'-O-(thiotriphosphate)tetralithium salt (ATP gamma S (1 mM) or alpha-beta-methylene ATP (1 mM). Inclusion of adenosine 3',5'-cyclic monophosphate sodium salt (cAMP, 100 microM), guanosine 3',5'-cyclic monophosphate sodium salt (cGMP, 100 microM), 12-O-tetradecanoylphorbol-13-acetate (TPA, 1 microM) or phorbol-12,13-dibutyrate (1 microM) in the intracellular solution did not affect the facilitation. Guanosine 5'-O-(thiotriphosphate)tetralithium salt (GTP gamma S, 500 microM) or guanosine 5'-O(2-thiodiphosphate)-trilithium salt (GDP beta S, 500 microM) did not modify the facilitation either.(ABSTRACT TRUNCATED AT 250 WORDS)