[ 3H]Batrachotoxinin A-20-α-benzoate Binding in Synaptosomes from Susceptible and kdr-Type Resistant German Cockroaches, Blattella germanica (L.)

Synaptosomal binding of [ 3H]batrachotoxinin A-20-α-benzoate ([ 3H]BTX-B), a potent sodium channel toxin, was measured in kdr-type resistant (Ectiban-R) and susceptible (CSMA) German cockroaches. Previous studies indicated that the Ectiban-R strain was 8.7-fold cross-resistant to batrachotoxin. Scatchard analysis of [ 3H]BTX-B binding demonstrated that the resistant and susceptible strains have similar binding affinities ( K D values 230 and 252 n M) and binding site densities ( B max values, 6.0 and 7.6 pmol/mg protein). Batrachotoxin, aconitine, and veratridine displaced [ 3H]BTX-B binding in both strains with IC 50 values of 1.0-1.2, 18-19, and 73-77 μ M, respectively. The dihydropyrazole insecticide RH 3421 displaced [ 3H]BTX-B binding by 13% only at 10 μ M, the highest concentration examined. The pyrethroid insecticide deltamethrin had no effect on [ 3H]BTX-B binding in either strain. Our results indicate that the binding of site 2 neurotoxins to cockroach sodium channels is not altered in the kdr-type resistant strain. Possible molecular mechanisms of kdr-type resistance are discussed.