ROLE OF THE GTP-BINDING PROTEIN G(O) 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 invest igate the acute, in vitro effects of ethanol on the function of voltag e activated Ca2+ channels in cultured neurons derived from dorsal root ganglia (DRG) of embryonic mice. Although 5.4 mM ethanol produced a s ustained increase of the amplitude of the whole-cell Ca2+ current (I-C a), 43.2 mM ethanol had a time dependent biphasic effect. That is, wit hin 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 t he probability of single-channel open events. Pretreatment of DRG with 200 ng/ml of pertussis toxin abolished the inhibitory, but not the fa cilitatory, effect of 43.2 mM ethanol on I-Ca. Pretreatment with pertu ssis toxin also prevented the reduction of the probability of single-c hannel opening caused by 43.2 mM ethanol. Similarly, dialysis of neuro ns with polyclonal antibodies against the alpha-subunit of G(o) but no t G(s), abolished the inhibitory effect of 43.2 mM ethanol on I-Ca. Th ese data demonstrate concentration- and time-dependent biphasic effect s of ethanol on the activity of Ca2+ channels. The inhibitory effect o f ethanol requires activation of the alpha-subunit of G(o), which then decreases the probability of Ca2+ channel opening.