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.
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1 March 2004
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February 23 2004
Inhibition of the Collapse of the Shaker K+ Conductance by Specific Scorpion Toxins
Froylan Gómez-Lagunas,
Froylan Gómez-Lagunas
1Department of Physiology, School of Medicine, National Autonomous University of México, Ciudad Universitaria, México City D.F. 04510, México
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Cesar V.F. Batista,
Cesar V.F. Batista
2Department of Molecular Medicine and Bioprocesses, Institute of Biotechnology, National Autonomous University of México, Cuernavaca 62210, México
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Timoteo Olamendi-Portugal,
Timoteo Olamendi-Portugal
2Department of Molecular Medicine and Bioprocesses, Institute of Biotechnology, National Autonomous University of México, Cuernavaca 62210, México
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Martha E. Ramírez-Domínguez,
Martha E. Ramírez-Domínguez
2Department of Molecular Medicine and Bioprocesses, Institute of Biotechnology, National Autonomous University of México, Cuernavaca 62210, México
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Lourival D. Possani
Lourival D. Possani
2Department of Molecular Medicine and Bioprocesses, Institute of Biotechnology, National Autonomous University of México, Cuernavaca 62210, México
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Froylan Gómez-Lagunas
1Department of Physiology, School of Medicine, National Autonomous University of México, Ciudad Universitaria, México City D.F. 04510, México
Cesar V.F. Batista
2Department of Molecular Medicine and Bioprocesses, Institute of Biotechnology, National Autonomous University of México, Cuernavaca 62210, México
Timoteo Olamendi-Portugal
2Department of Molecular Medicine and Bioprocesses, Institute of Biotechnology, National Autonomous University of México, Cuernavaca 62210, México
Martha E. Ramírez-Domínguez
2Department of Molecular Medicine and Bioprocesses, Institute of Biotechnology, National Autonomous University of México, Cuernavaca 62210, México
Lourival D. Possani
2Department 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: [email protected]
Abbreviation used in this paper: SF, selectivity filter.
Received:
May 19 2003
Accepted:
January 23 2004
Online ISSN: 1540-7748
Print ISSN: 0022-1295
The Rockefeller University Press
2004
J Gen Physiol (2004) 123 (3): 265–279.
Article history
Received:
May 19 2003
Accepted:
January 23 2004
Citation
Froylan Gómez-Lagunas, Cesar V.F. Batista, Timoteo Olamendi-Portugal, Martha E. Ramírez-Domínguez, Lourival D. Possani; Inhibition of the Collapse of the Shaker K+ Conductance by Specific Scorpion Toxins . J Gen Physiol 1 March 2004; 123 (3): 265–279. doi: https://doi.org/10.1085/jgp.200308871
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