Role of the GTP-Binding Protein Go in the Suppressant Effect of Ethanol on Voltage-Activated Calcium Channels of Murine Sensory Neurons

Whole-cell and single-channel recording techniques were used to investigate the acute, in vitro effects of ethanol on the function of voltage-activated Ca²⁺ channels in cultured neurons derived from dorsal root ganglia (DRG) of embryonic mice. Although 5.4 MM ethanol produced a sustained increase of the amplitude of the whole-cell Ca²⁺ current (I_Ca), 43.2 mM ethanol had a time-dependent biphasic effect. That is, within 0.5 min of exposure to 43.2 MM ethanol, the maximal amplitude of I_Ca initially increased before declining to a new steady-state value. As anticipated, the facilitatory and inhibitory effects of ethanol on I_Ca were associated with an increase and decrease, respectively, in the probability of single-channel open events. Pretreatment of DRG with 200 ng/ml of pertussis toxin abolished the inhibitory, but not the facilitatory, effect of 43.2 mM ethanol on I_Ca Pretreatment with pertussis toxin also prevented the reduction of the probability of single-channel opening caused by 43.2 mM ethanol. Similarly, dialysis of neurons with polyclonal antibodies against the a-subunit of Go but not G., abolished the inhibitory effect of 43.2 mM ethanol on I_Ca These data demonstrate concentration- and time-dependent biphasic effects of ethanol on the activity of Ca²⁺ channels. The inhibitory effect of ethanol requires activation of the a-subunit of Go, which then decreases the probability of Ca²⁺ channel opening.