The organochlorine pesticides γ-hexachlorocyclohexane (lindane), α-endosulfan and dieldrin differentially interact with GABA A and glycine-gated chloride channels in primary cultures of cerebellar granule cells

Abstract

The neurotoxic organochlorine pesticides γ-hexachlorocyclohexane, α-endosulfan and dieldrin induce in mammals a hyperexcitability syndrome accompanied by convulsions. They reduce the GABA-induced Cl − flux. The strychnine-sensitive glycine receptor also regulates Cl −-flux inhibitory responses. We studied the effects of these compounds on Cl − channels associated with glycine receptors in cultured cerebellar granule cells in comparison to the GABA A receptor. Both GABA (EC 50: 5 μM) and glycine (EC 50: 68 μM) increased 36Cl − influx. This increase was antagonized by bicuculline and strychnine, respectively. Lindane inhibited with similar potency both GABA A (IC 50: 6.1 μM) and glycine (5.0 μM) receptors. α-Endosulfan and dieldrin inhibited the GABA A receptor (IC 50 values: 0.4 μM and 0.2 μM, respectively) more potently than the glycine receptor (IC 50 values: 3.5 μM and 3 μM, respectively). Picrotoxinin also inhibited the glycine receptor, although with low potency (IC 50>100 μM). A 3D pharmacophore model, consisting of five hydrophobic regions and one hydrogen bond acceptor site in a specific three-dimensional arrangement, was developed for these compounds by computational modelling. We propose that the hydrogen bond acceptor moiety and the hydrophobic region were responsible for the affinity of these compounds at the GABA A receptor whereas only the hydrophobic region of the molecules was responsible for their interaction with the glycine receptors. In summary, these compounds could produce neuronal hyperexcitability by blocking glycine receptors besides the GABA A receptor. We propose that two zones of the polychlorocycloalkane pesticide molecules (a lipophilic zone and a polar zone) differentially contribute to their binding to GABA A and glycine receptors.