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Interaction between quaternary ammonium ions in the pore of potassium channels. Evidence against an electrostatic repulsion mechanism.

Thompson J, Begenisich T - J. Gen. Physiol. (2000)

Bottom Line: This antagonism was absent in solutions with Rb(+) as the only permeant ion.An externally applied trivalent TEA analogue, gallamine, was less effective than the monovalent TEA in inhibiting block by internal TEA.We found that these results can be simulated by a simple 4-barrier-3-site permeation model in which ions compete for available binding sites without long-range electrostatic interactions.

View Article: PubMed Central - PubMed

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

ABSTRACT
We have examined the interaction between internal and external ions in the pore of potassium channels. We found that external tetraethylammonium was able to antagonize block of Shaker channels by internal TEA when the external and internal solutions contained K(+) ions. This antagonism was absent in solutions with Rb(+) as the only permeant ion. An externally applied trivalent TEA analogue, gallamine, was less effective than the monovalent TEA in inhibiting block by internal TEA. In addition, block by external TEA was little affected by changes in the concentration of internal K(+) ions, but was increased by the presence of internal Na(+) ions in the pore. These results demonstrate that external and internal TEA ions, likely located at opposite ends of the pore selectivity filter, do not experience a mutual electrostatic repulsion. We found that these results can be simulated by a simple 4-barrier-3-site permeation model in which ions compete for available binding sites without long-range electrostatic interactions.

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Interaction between external TEA and internal K+ ions. (Inset) Currents (at 0 mV) recorded with 135 mM (left) and 20 mM (right) internal K+ in the absence (larger current) and presence of 25 mM external TEA. (Main figure) Channel block (at 0 mV) at the indicated concentrations of external TEA in 135 mM (•) and 20 mM (□) internal K+. Block by 25 mM TEA was measured (▴) with 20 mM internal K+ and a nominally 0 K+ external solution (see methods).
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Figure 9: Interaction between external TEA and internal K+ ions. (Inset) Currents (at 0 mV) recorded with 135 mM (left) and 20 mM (right) internal K+ in the absence (larger current) and presence of 25 mM external TEA. (Main figure) Channel block (at 0 mV) at the indicated concentrations of external TEA in 135 mM (•) and 20 mM (□) internal K+. Block by 25 mM TEA was measured (▴) with 20 mM internal K+ and a nominally 0 K+ external solution (see methods).

Mentions: As noted in the introduction, the observed reduction in RBK1 channel block by external TEA with elevated internal K+ ions (Newland et al. 1992) is consistent with an electrostatic repulsion between these two ions. We have examined external TEA block of Shaker channels with different concentrations of internal K+ and some of these results are illustrated in Fig. 9.


Interaction between quaternary ammonium ions in the pore of potassium channels. Evidence against an electrostatic repulsion mechanism.

Thompson J, Begenisich T - J. Gen. Physiol. (2000)

Interaction between external TEA and internal K+ ions. (Inset) Currents (at 0 mV) recorded with 135 mM (left) and 20 mM (right) internal K+ in the absence (larger current) and presence of 25 mM external TEA. (Main figure) Channel block (at 0 mV) at the indicated concentrations of external TEA in 135 mM (•) and 20 mM (□) internal K+. Block by 25 mM TEA was measured (▴) with 20 mM internal K+ and a nominally 0 K+ external solution (see methods).
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2232892&req=5

Figure 9: Interaction between external TEA and internal K+ ions. (Inset) Currents (at 0 mV) recorded with 135 mM (left) and 20 mM (right) internal K+ in the absence (larger current) and presence of 25 mM external TEA. (Main figure) Channel block (at 0 mV) at the indicated concentrations of external TEA in 135 mM (•) and 20 mM (□) internal K+. Block by 25 mM TEA was measured (▴) with 20 mM internal K+ and a nominally 0 K+ external solution (see methods).
Mentions: As noted in the introduction, the observed reduction in RBK1 channel block by external TEA with elevated internal K+ ions (Newland et al. 1992) is consistent with an electrostatic repulsion between these two ions. We have examined external TEA block of Shaker channels with different concentrations of internal K+ and some of these results are illustrated in Fig. 9.

Bottom Line: This antagonism was absent in solutions with Rb(+) as the only permeant ion.An externally applied trivalent TEA analogue, gallamine, was less effective than the monovalent TEA in inhibiting block by internal TEA.We found that these results can be simulated by a simple 4-barrier-3-site permeation model in which ions compete for available binding sites without long-range electrostatic interactions.

View Article: PubMed Central - PubMed

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

ABSTRACT
We have examined the interaction between internal and external ions in the pore of potassium channels. We found that external tetraethylammonium was able to antagonize block of Shaker channels by internal TEA when the external and internal solutions contained K(+) ions. This antagonism was absent in solutions with Rb(+) as the only permeant ion. An externally applied trivalent TEA analogue, gallamine, was less effective than the monovalent TEA in inhibiting block by internal TEA. In addition, block by external TEA was little affected by changes in the concentration of internal K(+) ions, but was increased by the presence of internal Na(+) ions in the pore. These results demonstrate that external and internal TEA ions, likely located at opposite ends of the pore selectivity filter, do not experience a mutual electrostatic repulsion. We found that these results can be simulated by a simple 4-barrier-3-site permeation model in which ions compete for available binding sites without long-range electrostatic interactions.

Show MeSH
Related in: MedlinePlus