SAXITOXIN BINDING TO NEURAL MEMBRANES FROM PYRETHROID SUSCEPTIBLE AND RESISTANT TOBACCO BUDWORM MOTHS HELIOTHIS-VIRESCENS

1. [H-3]Saxitoxin, a sodium channel probe, was found to bind reversibly with high affinity to a single class of noninteracting sites in membrane preparations from whole head homogenates of tobacco budworm, Heliothis virescens (F.), moths from a pyrethroid susceptible strain and from a pyrethroid resistant strain with nerve insensitivity and metabolic resistance mechanisms. 2. No significant interstrain differences were detected in saturation (K(D), B(max)) and kinetic (k+1, k-1) experiments. 3. Also, five pyrethroids, two formamidines, and DDT had no significant effect on [H-3]saxitoxin binding when tested at concentrations of 1 x 10(-4) and 1 x 10(-8) M. 4. It appeared that a decreased density in sodium channels in resistant strain moths as compared with that in susceptible strain moths was not a factor in pyrethroid-induced resistance in this particular strain of tobacco budworm.