BLOCKING ACTIONS OF BIDN, A BICYCLIC DINITRILE CONVULSANT COMPOUND, ON WILD-TYPE AND DIELDRIN-RESISTANT GABA RECEPTOR HOMO-OLIGOMERS OF DROSOPHILA-MELANOGASTER EXPRESSED IN XENOPUS OOCYTES

The receptor antagonist actions are described for a novel bicyclic din itrile compound (BIDN, 3,3-bis-(trifluoromethyl)-bicyclo [2.2.1] hepta ne-2,2-dicarbonitrile) on a Drosophila melanogaster homo-oligomeric GA BA receptor expressed in Xenopus oocytes. BIDN blocked the wild-type f orm of the receptor in a neither purely competitive, nor purely non-co mpetitive manner, being dependent on the GABA concentration yet insurm ountable, and block was independent of the membrane potential. BIDN wa s found to be less effective against a mutant (A(302) --> S) form of t he receptor resistant to dieldrin and picrotoxinin. This cross resista nce of dieldrin-resistant receptors to BIDN is of interest in the ligh t of recent findings that BIDN binding to insect membranes is displace d competitively by dieldrin, but not by picrotoxinin.