Role and Source of ATP for Activation of Nonselective Cation Channels by AlF Complex in Guinea Pig Chromaffin Cells

Abstract.

Intracellular dialysis with the solution containing the G protein activator, AlF complex, induced an inward nonselective cation current (I _NS) at −55 mV in chromaffin cells. Amplitudes of I _NS induced by dialysis with ATP-free AlF solutions progressively diminished as cells were pretreated with cyanide, a mitochondrial inhibitor. After a 10-min pretreatment, generation of I _NS by the AlF complex depended on exogenous ATP delivered from pipette solution. The relationship between amplitudes of I _NS and concentrations of MgATP was well expressed by a rectangular hyperbola with an EC₅₀ of 0.265 mm. This result suggests that the cyanide treatment almost depleted ATP near the plasma membrane. On the other hand, a similar cyanide treatment of adrenal medullary preparations did not induce a marked decrease in cellular ATP content. GTP, ITP, or UTP could not substitute for ATP in generation of I _NS by the AlF complex. Similarly, the substitution of ATP with non- or poorly hydrolyzable ATP analogues did not aid in generating I _NS. Bath application of the kinase inhibitor, H-7 (100 μm), suppressed AlF-induced I _NS in a manner depending on intracellular Mg²⁺. We conclude that ATP is a prerequisite for generation of I _NS as a phosphoryl donor and that mitochondria is the main source of ATP.