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Affinity and location of an internal K+ ion binding site in shaker K channels.

Thompson J, Begenisich T - J. Gen. Physiol. (2001)

Bottom Line: In addition, block by external TEA was significantly enhanced by increases in the internal K+ concentration.The TEA site (at 0 internal K+) appeared to sense approximately 5% of the field from the internal end of the pore (essentially colocalized with the internal K+ site).These results lead to a refined picture of the number and location of ion binding sites at the inner end of the pore in Shaker K channels.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York 14642, USA.

ABSTRACT
We have examined the interaction between TEA and K+ ions in the pore of Shaker potassium channels. We found that the ability of external TEA to antagonize block of Shaker channels by internal TEA depended on internal K+ ions. In contrast, this antagonism was independent of external K+ concentrations between 0.2 and 40 mM. The external TEA antagonism of internal TEA block increased linearly with the concentration of internal K+ ions. In addition, block by external TEA was significantly enhanced by increases in the internal K+ concentration. These results suggested that external TEA ions do not directly antagonize internal TEA, but rather promote increased occupancy of an internal K+ site by inhibiting the emptying of that site to the external side of the pore. We found this mechanism to be quantitatively consistent with the results and revealed an intrinsic affinity of the site for K+ ions near 65 mM located approximately 7% into the membrane electric field from the internal end of the pore. We also found that the voltage dependence of block by internal TEA was influenced by internal K+ ions. The TEA site (at 0 internal K+) appeared to sense approximately 5% of the field from the internal end of the pore (essentially colocalized with the internal K+ site). These results lead to a refined picture of the number and location of ion binding sites at the inner end of the pore in Shaker K channels.

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Pictorial representation of ion binding sites in the pore of Shaker K channels. Shown is a representation of the KcsA crystal structure (Doyle et al. 1998) with two of the four chains removed for clarity. The KcsA structure was visualized by RasMol (see http://www.umass.edu/microbio/rasmol/index2.htm), exported to a drawing program, and (crudely) converted to the “bent S6” conformation of del Camino et al. 2000.
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Figure 7: Pictorial representation of ion binding sites in the pore of Shaker K channels. Shown is a representation of the KcsA crystal structure (Doyle et al. 1998) with two of the four chains removed for clarity. The KcsA structure was visualized by RasMol (see http://www.umass.edu/microbio/rasmol/index2.htm), exported to a drawing program, and (crudely) converted to the “bent S6” conformation of del Camino et al. 2000.

Mentions: Thus, we propose to have identified a fourth K+ site in the pore of Shaker channels as illustrated in the cartoon in Fig. 7. Shown is a representation of the pore in the KcsA K channel incorporating the “bent S6” structure of del Camino et al. 2000. The three small, dark spheres in the pore represent the three K+ sites in the KcsA crystal (Doyle et al. 1998). Our results suggest the existence of a fourth K+ ion binding site (dashed circle) at the innermost end of the pore. We place this site quite near the inner end of the pore consistent with the weak voltage dependence of K+ binding to this site and the weak intrinsic voltage dependence of TEA block. This site has a very low affinity for Rb+ ions but can, as indicated, bind either K+ or TEA, but not both.


Affinity and location of an internal K+ ion binding site in shaker K channels.

Thompson J, Begenisich T - J. Gen. Physiol. (2001)

Pictorial representation of ion binding sites in the pore of Shaker K channels. Shown is a representation of the KcsA crystal structure (Doyle et al. 1998) with two of the four chains removed for clarity. The KcsA structure was visualized by RasMol (see http://www.umass.edu/microbio/rasmol/index2.htm), exported to a drawing program, and (crudely) converted to the “bent S6” conformation of del Camino et al. 2000.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2233657&req=5

Figure 7: Pictorial representation of ion binding sites in the pore of Shaker K channels. Shown is a representation of the KcsA crystal structure (Doyle et al. 1998) with two of the four chains removed for clarity. The KcsA structure was visualized by RasMol (see http://www.umass.edu/microbio/rasmol/index2.htm), exported to a drawing program, and (crudely) converted to the “bent S6” conformation of del Camino et al. 2000.
Mentions: Thus, we propose to have identified a fourth K+ site in the pore of Shaker channels as illustrated in the cartoon in Fig. 7. Shown is a representation of the pore in the KcsA K channel incorporating the “bent S6” structure of del Camino et al. 2000. The three small, dark spheres in the pore represent the three K+ sites in the KcsA crystal (Doyle et al. 1998). Our results suggest the existence of a fourth K+ ion binding site (dashed circle) at the innermost end of the pore. We place this site quite near the inner end of the pore consistent with the weak voltage dependence of K+ binding to this site and the weak intrinsic voltage dependence of TEA block. This site has a very low affinity for Rb+ ions but can, as indicated, bind either K+ or TEA, but not both.

Bottom Line: In addition, block by external TEA was significantly enhanced by increases in the internal K+ concentration.The TEA site (at 0 internal K+) appeared to sense approximately 5% of the field from the internal end of the pore (essentially colocalized with the internal K+ site).These results lead to a refined picture of the number and location of ion binding sites at the inner end of the pore in Shaker K channels.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York 14642, USA.

ABSTRACT
We have examined the interaction between TEA and K+ ions in the pore of Shaker potassium channels. We found that the ability of external TEA to antagonize block of Shaker channels by internal TEA depended on internal K+ ions. In contrast, this antagonism was independent of external K+ concentrations between 0.2 and 40 mM. The external TEA antagonism of internal TEA block increased linearly with the concentration of internal K+ ions. In addition, block by external TEA was significantly enhanced by increases in the internal K+ concentration. These results suggested that external TEA ions do not directly antagonize internal TEA, but rather promote increased occupancy of an internal K+ site by inhibiting the emptying of that site to the external side of the pore. We found this mechanism to be quantitatively consistent with the results and revealed an intrinsic affinity of the site for K+ ions near 65 mM located approximately 7% into the membrane electric field from the internal end of the pore. We also found that the voltage dependence of block by internal TEA was influenced by internal K+ ions. The TEA site (at 0 internal K+) appeared to sense approximately 5% of the field from the internal end of the pore (essentially colocalized with the internal K+ site). These results lead to a refined picture of the number and location of ion binding sites at the inner end of the pore in Shaker K channels.

Show MeSH
Related in: MedlinePlus