Effect of charybdotoxin and leiurotoxon 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 Ca²⁺-dependent K⁺ current (I_c) responsible for action potential repolarization (IC₅₀ = 6 nM) while leiurotoxin I selectively blocked a small Ca²⁺-dependent K⁺ conductance (I_AHP) responsible for the slow afterhyperpolarization following an action potential (IC₅₀ = 7.5 nM) in bullfrog sympathetic ganglion neurons. Neither of the toxins had a significant effects on other K⁺ currents (M-current [I_M], A-current [I_A] and the delayed rectifier [I_KD] 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 I_AHP in central neurons suggests that the channels underlying slow AHPs in those neurons are pharmacologically distinct from analogous channels in peripheral neurons.