Abstract

We examined the effect of Waglerin-1, a peptide of 22 amino acid residues purified from the venom of Wagler’s pit viper (Trimeresurus wagleri), on the whole cell current response (I_GABA) of freshly isolated murine hypothalamic neurons to γ-aminobutyric acid (GABA). Although the application of 32 μM Waglerin-1 alone had no effect on membrane conductance, coapplication with GABA increased I_GABA for 78 and suppressed I_GABA for 44 of the 141 neurons examined. The potentiating effect of Waglerin-1 was associated with a leftward shift of the concentration-response relation of GABA without increasing peak I_GABA. This potentiating effect of Waglerin-1 on I_GABA mimics diazepam. Furthermore, the benzodiazepine antagonist flumazenil antagonized Waglerin-1 potentiation of I_GABA. These observations suggest that Waglerin-1 acts on the benzodiazepine site of one type of GABA_Areceptor/channel complex to increase its affinity for agonist. In contrast, the depressant effect of Waglerin-1 was associated with a rightward shift of the concentration-response relation of GABA without depressing the maximal I_GABA; this suggests a competitive inhibition of a second class of GABAR. The ability of Waglerin-1 to suppress I_GABA showed a positive correlation with a similar action of Zn⁺⁺. As with Zn⁺⁺, the depressant effect of Waglerin-1 on I_GABA was more pronounced at negative holding potentials. These observations are discussed in terms of variation in the subunit composition of GABA receptors that murine central nervous system neurons express.