Effect of charybdotoxin and leiurotoxin I on potassium currents in bullfrog sympathetic ganglion and hippocampal neurons.

The effects of charybdotoxin and leiurotoxin I were examined on several classes of K+ currents in bullfrog sympathetic ganglion and hippocampal CA1 pyramidal neurons. Highly purified preparations of charybdotoxin selectively blocked a large voltage- and Ca(2+)-dependent K+ current (IC) responsible for action potential repolarization (IC50 = 6 nM) while leiurotoxin I selectively blocked a small Ca(2+)-dependent K+ conductance (IAHP) responsible for the slow afterhyperpolarization following an action potential (IC50 = 7.5 nM) in bullfrog sympathetic ganglion neurons. Neither of the toxins had significant effects on other K+ currents (M-current [IM], A-current [IA] and the delayed rectifier [IK]) present in these cells. Leiurotoxin I at a concentration of 20 nM had no detectable effect on currents in hippocampal CA1 pyramidal neurons. This lack of effect on IAHP in central neurons suggests that the channels underlying slow AHPs in those neurons are pharmacologically distinct from analogous channels in peripheral neurons.