Effect of Intracellular Dialysis of ATP on the Hyperpolarization-Activated Cation Current in Rat Dorsal Root Ganglion Neurons

Abstract

The mechanism of the effect of intracellular ATP on the hyperpolarization-activated non-selective cation current ( Ih) in rat dorsal root ganglion neurons was investigated using a whole cell voltage-clamp technique. Under voltage-clamp conditions, Ihwas activated by hyperpolarizing pulses raised to a voltage of between –70 and –130 mV. The activation curve of Ihin rat dorsal root ganglion (DRG) neurons shifted by about 15 mV in the positive direction with an intracellular solution containing 1 mM cAMP. When ATP (2 mM) was applied intracellularly, the half-maximal activation voltage ( Vhalf) of Ihshifted from –97.4 ± 1.9 to –86.8 ± 1.6 mV, resulting in an increase in the current amplitude of Ihby the pulse to between –80 and –90 mV. In the presence of an adenylate cyclase inhibitor, SQ-22536 (100 μM), the intracellular dialysis of ATP also produced a shift in the voltage-dependence of Ihin rat DRG neurons, indicating that the effect of ATP was not caused by cAMP converted by adenylate cyclase. Intracellular dialysis of a nonhydrolysable ATP analog, AMP-PNP or ATP-γ-S, also produced a positive shift in the voltage-dependence of Ihactivation, suggesting that the effect of ATP results from its direct action on the channel protein. These results indicate that cytosolic ATP directly regulates the voltage dependence of Ihactivation as an intracellular modulating factor.