Komagiri, You and Naoki Kitamura. Effect of intracellular dialysis of ATP on the hyperpolarization-activated cation current in rat dorsal root ganglion neurons. . 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

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... 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 Ϯ 1.9 to -86.8 Ϯ 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 M), 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. M E T H O D S Cell culture Rat DRG neurons were isolated from adult male Sprague-Dawley rats (7-12 wk old), using procedures that have been reported previously (Kim et al. 1980; Yong et al. 1988 ).