Binding of [3H]batrachotoxinin A-20-alpha-benzoate to a high affinity site associated with house fly head membranes.
1. [3H]Batrachotoxinin A-20-alpha-benzoate (BTX-B), a radioligand that labels the alkaloid activator recognition site of the voltage-sensitive sodium channel, was bound specifically to high affinity, saturable sites in a subcellular preparation from house fly (Musca domestica L.) heads that was shown previously to contain binding sites for other sodium channel-directed ligands. 2. Specific binding of [3H]BTX-B was observed in the presence of 140 mM sodium or potassium and was inhibited by choline ion. 3. Saturating concentrations of scorpion (Leiurus quinquestriatus) venom stimulated the specific binding of [3H]BTX-B four-fold, increasing the proportion of specific binding of 10 nM [3H]BTX-B from less than 15% to 40%. Equilibrium dissociation studies in the presence of scorpion venom gave an equilibrium dissociation constant (KD) for [3H]BTX-B of 80 nM and a maximal binding capacity (Bmax) of 1.5 pmol/mg protein. 4. Parallel experiments in the absence of venom gave a KD value of 140 nM and a Bmax of 1.3 pmol/mg protein, indicating that scorpion venom stimulated [3H]BTX-B binding by increasing the affinity of this site approximately two-fold. 5. The specific binding of [3H]BTX-B was inhibited by the sodium channel activators aconitine and batrachotoxin and, to a lesser extent, by the anticonvulsant diphenylhydantoin. However, several other sodium channel-directed neurotoxins known to exert allosteric effects on the binding of [3H]BTX-B to mammalian brain preparations did not affect the binding of [3H]BTX-B to house fly head membranes.(ABSTRACT TRUNCATED AT 250 WORDS)
Soderlund
D M
DM
Department of Entomology, Cornell University, Geneva, NY 14456.
Grubs
R E
RE
Adams
P M
PM
D000818:Animals; D001496:Batrachotoxins / Q000378:metabolism*; D006257:Head; D006793:Houseflies / Q000378:metabolism*; D008566:Membranes / Q000378:metabolism; D009498:Neurotoxins / Q000378:metabolism*; D011950:Receptors, Cholinergic / Q000378:metabolism*; D012604:Scorpion Venoms / Q000494:pharmacology; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism
D001496:Batrachotoxins; D009498:Neurotoxins; D011950:Receptors, Cholinergic; D012604:Scorpion Venoms; D015222:Sodium Channels; C041417:batrachotoxin receptor; C031775:batrachotoxinin A 20-alpha-benzoate