Binding of [3H]batrachotoxinin A-20-alpha-benzoate and [3H]saxitoxin to receptor sites associated with sodium channels in trout brain synaptoneurosomes.
1. [3H]Batrachotoxinin A-20-alpha-benzoate ([3H]BTX-B) and [3H]saxitoxin ([3H]STX), radioligands that bind to distinct sites on the voltage-sensitive sodium channel, were bound specifically to saturable sites in rainbow trout (Oncorhynchus mykiss) brain synaptoneurosomes. 2. Specific [3H]BTX-B binding was temperature dependent with highest levels of specific [3H]BTX-B binding observed at 7 degrees C. Specific binding was inversely correlated with assay temperature at temperatures above 7 degrees C. 3. Saturating concentrations of scorpion (Leiurus quinquestriatus) venom (ScV) stimulated specific [3H]BTX-B binding at 27 degrees C, but not at 7 degrees C. The dihydropyrazole insecticide RH 3421 inhibited specific [3H]BTX-B binding at 7 degrees C but had no effect on specific binding at 27 degrees C. The sodium channel activators veratridine and aconitine and the local anesthetic dibucaine inhibited specific [3H]BTX-B binding at both 7 degrees C and 27 degrees C. 4. Displacement experiments in the presence of ScV at 27 degrees C gave an equilibrium dissociation constant (KD) for [3H]BTX-B of 710 nM and a maximal binding capacity (Bmax) of 11.3 pmol/mg protein. Kinetic experiments established the rates of association (1.17 x 10(5) min-1 nM-1) and dissociation (0.0514 min-1) of the ligand-receptor complex. 5. The binding of [3H]STX reached apparent saturation at 7.5 nM. Scatchard analysis of the saturation data indicated a KD of 3.8 nM and a Bmax of 1.9 pmol/mg protein. 6. These studies provide evidence for high affinity, saturable binding sites for [3H]BTX-B and [3H]STX in trout brain preparations. Whereas certain neurotoxins modified the specific binding of [3H]BTX-B in trout brain synaptoneurosomes in a predictable fashion, other compounds known to affect specific [3H]BTX-B binding in mammalian brain preparations had no effect on specific [3H]BTX-B binding in the trout.
Rubin
J G
JG
Department of Entomology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456.
Soderlund
D M
DM
D000818:Animals; D001496:Batrachotoxins / Q000378:metabolism; D001665:Binding Sites / Q000187:drug effects; D007306:Insecticides / Q000494:pharmacology*; D009570:Nitriles; D011722:Pyrethrins / Q000494:pharmacology*; D011869:Radioligand Assay; D012530:Saxitoxin / Q000378:metabolism; D015222:Sodium Channels / Q000378:metabolism*; D013574:Synaptosomes / Q000187:drug effects*; D014316:Tritium; D014337:Trout / Q000378:metabolism*
D001496:Batrachotoxins; D007306:Insecticides; D009570:Nitriles; D011722:Pyrethrins; D015222:Sodium Channels; D014316:Tritium; C017180:decamethrin; D012530:Saxitoxin; C031775:batrachotoxinin A 20-alpha-benzoate