EFFECTS OF PLANT DITERPENES ON THE NEURONAL GABA(A) RECEPTOR-OPERATEDCHLORIDE CURRENT

THE effects of plant diterpenes, horminone (HMN) and taxodione (TXN), on the GABA(A) receptor-operated Cl- current (I-GABA) were investigate d in voltage-clamped and internally perfused neurones dissociated from frog dorsal root ganglia. Both diterpenes depressed I-GABA in a conce ntration-dependent manner similar to that of picrotoxin. Concentration s required to elicit 50% depression of the I-GABA were 10(-6) M for pi crotoxin, 10(-5) M for HMN and 10(-4) M for TXN. Blocking and restorat ion kinetics of the I-GABA with HMN were also similar to those of picr otoxin. Time constants for both the blockade and restoration of the I- GABA with TXN were more than five times greater than those with HMN.