[The pharmacology of the GABA-induced biphasic response in guinea-pig celiac ganglion neurons in vitro].

In guinea-pig celiac ganglion neurons, GABA induced a biphasic response, i.e. a depolarizing response associated with a resistance decrease followed by a hyperpolarizing response associated with a resistance increase. Such response persisted in low Ca2+ high Mg2+ medium. The GABA-induced biphasic response was mimicked by muscimol and inhibited by bicuculline methiodide (100 mumol/L) and picrotoxin (100-300 mumol/L). At doses producing almost equal depolarizing responses, muscimol was weaker in producing hyperpolarizing responses than GABA. Baclofen had no effect on membrane potentials of the ganglion cells. These results suggest that the depolarizing phase of the GABA-induced biphasic response is mediated by GABAA/Cl- ionophore receptor complex and the hyperpolarizing phase may be mediated by a novel type of GABA receptor possessing similar pharmacological properties as the classical GABAA receptor.