Saxitoxin binding to neural membranes from pyrethroid susceptible and resistant tobacco budworm moths Heliothis virescens

Abstract

1. [ 3H]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 [ 3H]saxitoxin binding when tested at concentrations of 1 × 10 −4 and 1 × 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.