The Journal of General Physiology
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Published online Feb 23 2004. doi:10.1085/jgp.200308871
The Rockefeller University Press, 0022-1295 $8.00
JGP, Volume 123, Number 3, 265-279
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Inhibition of the Collapse of the Shaker K+ Conductance by Specific Scorpion Toxins

Froylan Gómez-Lagunas1, Cesar V.F. Batista2, Timoteo Olamendi-Portugal2, Martha E. Ramírez-Domínguez2, and Lourival D. Possani2

1 Department of Physiology, School of Medicine, National Autonomous University of México, Ciudad Universitaria, México City D.F. 04510, México
2 Department of Molecular Medicine and Bioprocesses, Institute of Biotechnology, National Autonomous University of México, Cuernavaca 62210, México

Address correspondence to Froylan Gómez-Lagunas, Department Fisiologia, Edificio de Investigacion, 1er piso, Facultad de Medicina, University of México, Ciudad Universitaria, Apartado, Postal 70-250 México City D.F. 04510, México. Fax: (52) 777-3172388; email: froylan{at}ibt.unam.mx

The Shaker B K+ conductance (GK) collapses when the channels are closed (deactivated) in Na+ solutions that lack K+ ions. Also, it is known that external TEA (TEAo) impedes the collapse of GK (Gómez-Lagunas, F. 1997. J. Physiol. 499:3–15; Gómez-Lagunas, F. 2001. J. Gen. Physiol. 118:639–648), and that channel block by TEAo and scorpion toxins are two mutually exclusive events (Goldstein, S.A.N., and C. Miller. 1993. Biophys. J. 65:1613–1619). Therefore, we tested the ability of scorpion toxins to inhibit the collapse of GK in 0 K+. We have found that these toxins are not uniform regarding the capacity to protect GK. Those toxins, whose binding to the channels is destabilized by external K+, are also effective inhibitors of the collapse of GK. In addition to K+, other externally added cations also destabilize toxin block, with an effectiveness that does not match the selectivity sequence of K+ channels. The inhibition of the drop of GK follows a saturation relationship with [toxin], which is fitted well by the Michaelis-Menten equation, with an apparent Kd bigger than that of block of the K+ current. However, another plausible model is also presented and compared with the Michaelis-Menten model. The observations suggest that those toxins that protect GK in 0 K+ do so by interacting either with the most external K+ binding site of the selectivity filter (suggesting that the K+ occupancy of only that site of the pore may be enough to preserve GK) or with sites capable of binding K+ located in the outer vestibule of the pore, above the selectivity filter.

Key Words: ion channel • conductance • Shaker • toxin • zero-K+

Abbreviation used in this paper: SF, selectivity filter.


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F. Gomez-Lagunas
Stability of the Shab K+ Channel Conductance in 0 K+ Solutions: The Role of the Membrane Potential
Biophys. J., December 15, 2007; 93(12): 4197 - 4208.
[Abstract] [Full Text] [PDF]


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