M‐type K+ current inhibition by a toxin from the scorpion Buthus eupeus

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Abstract
A number of invertebrate venoms have been tested for effects on M‐type K+ currents (I K(M)) in differentiated mouse neuroblastoma X rat glioma NG108‐15 cells. Among the venoms tested, Buthus eupeus scorpion venom reversibly inhibited I K(M) by ∼ 44% at 50 μg/ml. Inhibition was not due to activation of bradykinin or nucleotide (pyrymidine) receptors. On venom fractionation, a polypeptide of 4 kDa was purified that inhibited I K(M) by ∼45% with an IC50 of ∼;33 nM. Neither the crude venom nor the purified polypeptide affected the Ca2+ current or the delayed rectifier K+ current. While the crude venom prolonged the Na+ current, the polypeptide did not. Thus, the 4 kDa Buthus eupeus polypeptide appears to be a selective inhibitor of I K(M) in NG108‐15 cells.