Radioligand binding displacement studies were conducted to determine the effects of Type I and II pyrethroids on [3H]flunitrazepam (FLU), [3H]muscimol (MUS), and [35S]t-butylbicyclophosphorothionate (TBPS) binding. Competition experiments with [3H]FLU and [3H]MUS indicate a lack of competition for binding by the pyrethroids. Type I pyrethroids failed to compete for the binding of [35S]TBPS at concentrations as high as 50 μM. Type II pyrethroids inhibited [35S]TBPS binding to rat brain synaptosomes with Ki, values ranging from 5-10 μM. The data presented here suggest that the interaction of Type II pyrethroids with the γ-aminobutyric acid (GABA) receptor-ionophore complex is restricted to a site near the TBPS/picrotoxinin binding site.
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