A NOVEL TOXIN FROM THE SCORPION ANDROCTONUS-AUSTRALIS BLOCKS SHAKER K+ CHANNELS EXPRESSED IN XENOPUS OOCYTES

The Shaker B potassium channel expressed in Xenopus laevis oocytes is blocked, in a total reversible manner from the outside part, by a new toxin (Aa1) composed of 40 amino acid residues, purified from the veno m of the North African scorpion Androctonus australis Garzoni. The exp eriments were performed with patch-clamp technique in the outside-out configuration. The half blocking concentration is approximately 4.5 mu M with a 1:1 stoichiometry. The activation and inactivation kinetics of the current are not modified by the blocking mechanism. The binding affinity is not voltage dependent. These results suggest a simple bim olecular mechanism of blockade by which the toxin occludes the externa l vestibule of the channel and thereby inhibits the K+ ions conduction . (C) 1998 Academic Press.