Effects of histrionicotoxin derivatives on ion channels and acetylcholine receptor-channel complexes in bullfrog sympathetic ganglia.

1. Four synthetic histrionicotoxin derivatives (H8-, H12-, C4H10- and C5H10-HTX) were applied to bullfrog (Rana catesbeiana) sympathetic ganglia and their effects were compared electrophysiologically. 2. The derivatives (60-100 microM) blocked both acetylcholine receptor-channel complex (ACh RC complex) and Na+ channel to cause a transmission failure. They also blocked K+ and Ca2+ channels. 3. Although all 4 derivatives exhibited similar effects, their potencies on respective ionic channels differed from one another. 4. Two types of (presumably subsynaptic and extrasynaptic) ACh RC complexes in ganglion cells were distinguished based on their differential sensitivities to HTX derivatives.