Inhibition of t-[35S]butylbicyclophosphorothionate binding by convulsant agents in primary cultures of cerebellar neurons.

The characteristics of the picrotoxinin binding site present on the gamma-aminobutyric acidA (GABAA) receptor were studied in neurons using primary cultures of cerebellar granule cells. The binding properties of these sites in intact cultured cells were compared with those measured in cultured cell membrane preparations. t-[35S]Butylbicyclophosphorothionate (TBPS) binding was performed in cultured rat cerebellar neurons grown for 13 days. Binding parameters (Kd and Bmax) were similar to those reported in the literature determined using brain membranes. However, equilibrium was reached faster when using intact cultured neurons. Convulsant compounds like picrotoxinin (PTX) and pentylenetetrazol (PTZ) competitively inhibited the binding of TBPS in this in vitro system. Convulsant organochlorine pesticides (gamma-hexachlorocyclohexane gamma-HCH or lindane and the cyclodienes aldrin, endrin, dieldrin and alpha-endosulfan) competitively inhibited [35S]TBPS binding in cerebellar neuronal cultures. Inhibitory affinity constant (Ki) values were in the nanomolar range, alpha-endosulfan and endrin being the most potent inhibitors corresponding to their high toxicity in mammals. Stereospecificity was also shown for HCH isomers, the non-convulsant isomers (alpha- and delta-HCH) being 15-30 times less potent in inhibiting [35S]TBPS binding than the convulsant gamma-HCH, while the beta-isomer was inactive.