INHIBITION OF T-[S-35]BUTYLBICYCLOPHOSPHOROTHIONATE BINDING BY CONVULSANT AGENTS IN PRIMARY CULTURES OF CEREBELLAR NEURONS

The characteristics of the picrotoxinin binding site present on the ga mma-aminobutyric acid(A) (GABA(A)) receptor were studied in neurons us ing primary cultures of cerebellar granule cells. The binding properti es of these sites in intact cultured cells were compared with those me asured in cultured cell membrane preparations. t-[S-35]Butylbicyclopho sphorothionate (TBPS) binding was performed in cultured rat cerebellar neurons grown for 13 days. Binding parameters (K(d) and B(max)) were similar to those reported in the literature determined using brain mem branes. However, equilibrium was reached faster when using intact cult ured neurons. Convulsant compounds like picrotoxinin (PTX) and pentyle netetrazol (PTZ) competitively inhibited the binding of TBPS in this i n vitro system. Convulsant organochlorine pesticides (gamma-hexachloro cyclohexane gamma-HCH or lindane and the cyclodienes aldrin, endrin, d ieldrin and alpha-endosulfan) competitively inhibited [S-35]TBPS bindi ng in cerebellar neuronal cultures. Inhibitory affinity constant (K(i) ) values were in the nanomolar range, alpha-endosulfan and endrin bein g the most potent inhibitors corresponding to their high toxicity in m ammals. Stereospecificity was also shown for HCH isomers, the non-conv ulsant isomers (alpha-and delta-HCH) being 15-30 times less potent in inhibiting [S-35]TBPS binding than the convulsant gamma-HCH, while the beta-isomer was inactive.