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

Laboratory of Physiology, Department of Biomedical Sciences, the Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan

Submitted 8 May 2003; accepted in final form 1 July 2003

The mechanism of the effect of intracellular ATP on the hyperpolarization-activated non-selective cation current (I_h) in rat dorsal root ganglion neurons was investigated using a whole cell voltage-clamp technique. Under voltage-clamp conditions, I_h was activated by hyperpolarizing pulses raised to a voltage of between –70 and –130 mV. The activation curve of I_h in 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 (V_half) of I_h shifted from –97.4 ± 1.9 to –86.8 ± 1.6 mV, resulting in an increase in the current amplitude of I_h by 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 I_h in 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--S, also produced a positive shift in the voltage-dependence of I_h activation, 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 I_h activation as an intracellular modulating factor.

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