A novel toxin form 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 venom of the North African scorpion Androctonus australis Garzoni. The experiments were performed with patch-clamp technique in the outside-out configuration. The half blocking concentration is approximately 4.5 microM 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 bimolecular mechanism of blockade by which the toxin occludes the external vestibule of the channel and thereby inhibits the K+ ions conduction.
Pisciotta
M
M
Instituto di Cibernetica e Biofisica, CNR, Genova, Italy.
Ottolia
M
M
Possani
L D
LD
Prestipino
G
G
D000818:Animals; D004594:Electrophysiology; D015870:Gene Expression / Q000235:genetics; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects*; D012604:Scorpion Venoms / Q000302:isolation & purification* / Q000494:pharmacology; D051637:Shaker Superfamily of Potassium Channels; D014118:Toxins, Biological / Q000302:isolation & purification* / Q000494:pharmacology; D014982:Xenopus laevis
D015221:Potassium Channels; D012604:Scorpion Venoms; D051637:Shaker Superfamily of Potassium Channels; D014118:Toxins, Biological