Ethanol inhibition of L-type Ca 2+ channels in PC12 cells: role of permeant ions

Abstract

The effects of acute ethanol exposure on voltage-activated Ca 2+ channels in undifferentiated pheochromocytoma (PC12) cells were investigated using whole-cell patch clamp techniques. Concentrations of ethanol (5, 25 and 50 mM), at or below blood alcohol levels which constitute legal intoxication significantly reduced Ca 2+ currents evoked from a holding potential of −30 mV. Ethanol-induced inhibition of current was voltage-dependent in some cases, but this was not consistently observed. Inhibition of currents was reversible and was not due to an osmotic effect. The non-inactivating nature of the current, the inhibition of the current by nifedipine, and the lack of inhibition by ω-conotoxin, indicated that the current was carried through high-voltage activated, L-type Ca 2+ channels. Since intracellular Ca 2+ levels were highly buffered by exchange with the contents of the patch pipet, ethanol-induced inhibition of currents in PC12 cells is not likely to involve either a change in driving force due to a change in intracellular Ca 2+ levels or potentiation of Ca 2+-dependent Ca 2+ channel inactivation by the influx of Ca 2+. The degree of inhibition by 25 mM ethanol was the same when either Ca 2+, Ba 2+ or Na + was used as the current-carrying ion. This equivalency suggests that the channel's ion selectivity filter is not a site of action for ethanol.