Effects of [³H]‐BIDN, a novel bicyclic dinitrile radioligand for GABA‐gated chloride channels of insects and vertebrates

Abstract

3 Rat brain membranes were also shown to possess a population of saturable, speci®c [ 3 H]-BIDN binding sites, though of lower a nity than in rootworm and with a di erent pharmacological pro®le. Of the insecticidal GABAergic convulsants that displaced [ 3 H]-BIDN from rootworm, cockroach (Periplaneta americana) and rat brain membranes, many were more e ective in rootworm. 4 Functional GABA-gated chloride channels of rootworm nervous system and of cockroach nerve and muscle were blocked by BIDN, whereas cockroach neuronal GABA B receptors were una ected. 5 Expression in Xenopus oocytes of either rat brain mRNA, or cDNA-derived RNA encoding a GABA receptor subunit (Rdl) that is expressed widely in the nervous system of Drosophila melanogaster resulted in functional, homo-oligomeric GABA receptors that were blocked by BIDN. Thus, BIDN probes a novel site on GABA-gated Cl 7 channels to which a number of insecticidally-active molecules bind.

Structural model for γ-aminobutyric acid receptor noncompetitive antagonist binding: Widely diverse structures fit the same site

“…Important radioligands in these developments are [ 3 H]dihydroPTX (4,11), [ 35 S]tbutylbicyclophosphorothionate (TBPS) (5,12), [ 3 H]1-(4-ethynylphenyl)-4-n-propyl-2,6,7-trioxabicyclo[2.2.2]octane (EBOB) (6), and [ 3 H]3,3-bis-trif luoromethyl-bicyclo[2,2,1]heptane-2,2-dicarbonitrile (BIDN) (8) (Fig. 1A).…”

“…All of these insecticides and the botanical picrotoxinin (PTX) have widely diverse chemical structures but appear to act at the same nerve target. It is therefore important to understand how these compounds work in mammals and insects, or how they do not work when resistant insect strains appear.The GABA-gated chloride channel is the target for the insecticides and toxicants referred to above based on radioligand binding and electrophysiology studies (3)(4)(5)(6)(7)(8)(9)(10) (Fig. 1A).…”

“…The GABA-gated chloride channel is the target for the insecticides and toxicants referred to above based on radioligand binding and electrophysiology studies (3)(4)(5)(6)(7)(8)(9)(10) (Fig. 1A).…”

“…The GABA-gated chloride channel is the target for the insecticides and toxicants referred to above based on radioligand binding and electrophysiology studies (3)(4)(5)(6)(7)(8)(9)(10). Important radioligands in these developments are [ 3 H]dihydroPTX (4,11), [ 35 S]tbutylbicyclophosphorothionate (TBPS) (5,12), [ 3 H]1-(4-ethynylphenyl)-4-n-propyl-2,6,7-trioxabicyclo[2.2.2]octane (EBOB) (6), and [ 3 H]3,3-bis-trif luoromethyl-bicyclo[2,2,1]heptane-2,2-dicarbonitrile (BIDN) (8) (Fig.…”

“…The mutants were used to identify Cys residues undergoing disulfide cross-linking as a guide to channel pore structure (28). Next, [ 3 H]EBOB and [ 3 H]BIDN were used to identify positions where mutation altered binding (6,8). Finally, modeling of the NCA-binding domain (29, 30) was applied to the ␤ 3 homopentamer to determine whether the wide diversity of NCAs could fit the same site.…”