Influence of formamidines on batrachotoxin in a 20α-benzoate binding to neural membranes from pyrethroid susceptible and resistant tobacco budworm moths Heliothis virescens

1. Amitraz stimulated [³H]batrachotoxin in A 20-α-benzoate ([³H]BTX-B) binding to neural membranes from pyrethroid susceptible (S) and resistant (R) tobacco budworm moths, but N′-(2,4-xylyl)-N-methylformamidine (SN 49844) stimulated binding only with S moths.

2. Chlordimeform stimulated [³H]BTX-B binding only with R moths, and N-(4-chloro-o-tolyl)-N-methylformamidine (demethylchlordimeform) yielded no significant stimulation with either strain.

3. A mixture of amitraz and deltamethrin, a pyrethroid that previously had been shown to enhance [³H]BTX-B binding with tobacco budworm moths, also gave significant stimulation of radioligand binding with S moths.

4. When membranes were prepared from S moths at various intervals following topical application of amitraz, deltamethrin, or a mixture of amitraz and deltamethrin, biphasic stimulation of [³H]BTX-B binding was observed, with maximum enhancement occurring at 2 and 6 hr.

5. These results provided a basis for suggesting that a formamidine binding site is located on or closely associated with the sodium channel protein.

6. Whether this site is the same as the pyrethroid/DDT binding domain remains to be demonstrated; however, similarities in responses elicited by amitraz and deltamethrin alone and in combination indicate that some relationship may exist.