Pandinus imperator Scorpion Venom Blocks Voltage-Gated Potassium Channels in Nerve Fibers

We have examined the effects of venom from the scorpion Pandinus imperator on the membrane currents of voltage-clamped frog myelinatecl nerve fibers using the Vaseline-gap method. Crude venom, applied externally in concentra-tions from 50 to 500 fig/ml, selectively blocked the voltage-gated potassium currents without affecting nodal sodium currents or resting conductances. Block of potassium chan-nels by Pandinus venom was highly dependent on the mem-brane voltage, being greater at negative potentials than at positive potentials. The blocking effects of Pandinus venom were irreversible on the time scale of our experiments; how-ever, even high concentrations of venom failed to block po-tassium currents completely at positive potentials. These results suggest that Pandinus venom contains a compo-nent(s) that interacts specifically and strongly with a sub