Properties of α-bungarotoxin binding cholinergic receptors in pyrethroid susceptible and resistant tobacco budworm moths

Abstract

1. In membrane preparations from whole head homogenates of tobacco budworm, Heliothis virescens (F.), moths from a pyrethroid susceptible (S) strain and from a pyrethroid resistant (R) strain with multiple resistance mechanisms including nerve insensitivity, the nicotinic acetylcholine receptor antagonist [ 125I]-α-bungarotoxin (BGT) was found to bind reversibly with high affinity to a single class of noninteracting high density sites. Although no significant interstrain differences were found in saturation experiments with regard to radioligand affinity and number of binding sites, half-times for [ 125I]BGT dissociation were about 3 min longer in S than in R moth preparations. 2. Nicotinic drugs generally were more potent than muscarinic drugs in displacing bound [ 125I]BGT from membranes of both strains. There were no significant interstrain differences with d-tubocurarine, decamethonium, (±)-quinuclidinyl benzilate, and (−)-scopolamine; however, (−)-nicotine (by 10×) and atropine (by 2×) were more potent in displacing [ 125I]BGT bound to membrane from S than from R moths. 3. Five pyrethroids, four formamidines, and one carbamate were without significant effect on [ 125I]BGT binding in membranes from both strains when tested at concentrations of 1 × 10 −5 and 1 × 10 −7 M. However, DDT at 1 × 10 −5 M gave about 20% stimulation of [ 125I]BGT binding in preparations from S moths. 4. It was concluded that [ 125I]BGT was binding to populations of nicotinic receptors in membranes from S and R moths. Although some differences may exist in the nature of the receptors between the two strains, studies with insecticides did not provide any basis for associating nerve insensitivity resistance to pyrethroids with tobacco budworm moth nicotinic receptors as probed with [ 125I]BGT.