Permeant Anions Control Gating of Calcium-dependent Chloride Channels

Permeant Anions Control Gating of Calcium-dependent Chloride Channels The effects of external anions (SCN−, NO 3 − , I−, Br−, F−, glutamate, and aspartate) on gating of Ca2+-dependent Cl− channels from rat parotid acinar cells were studied using the whole-cell configuration of the patch-clamp technique. Shifts in the reversal potential of the current induced by replacement of external Cl− with foreign anions, gave the following selectivity sequence based on permeability ratios (P x/P Cl): SCN−>I−>NO 3 − >Br−>Cl−>F−>aspartate>glutamate. Using a continuum electrostatic model we calculated that this lyotropic sequence resulted from the interaction between anions and a polarizable tunnel with an effective dielectric constant of ∼23. Our data revealed that anions with P x/PCl > 1 accelerated activation kinetics in a voltage-independent manner and slowed deactivation kinetics. Moreover, permeant anions enhanced whole-cell conductance (g, an index of the apparent open probability) in a voltage-dependent manner, and shifted leftward the membrane potential-g curves. All of these effects were produced by the anions with an effectiveness that followed the selectivity sequence. To explain the effects of permeant anions on activation kinetics and g Cl we propose that there are 2 different anion-binding sites in the channel. One site is located outside the electrical field and controls channel activation kinetics, while a second site is located within the pore and controls whole-cell conductance. Thus, interactions of permeant anions with these two sites hinder the closing mechanism and stabilize the channel in the open state. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

Permeant Anions Control Gating of Calcium-dependent Chloride Channels

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Publisher
Springer-Verlag
Copyright
Copyright © 2004 by Springer-Verlag
Subject
Life Sciences; Human Physiology; Biochemistry, general
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s00232-004-0659-x
Publisher site
See Article on Publisher Site

Abstract

The effects of external anions (SCN−, NO 3 − , I−, Br−, F−, glutamate, and aspartate) on gating of Ca2+-dependent Cl− channels from rat parotid acinar cells were studied using the whole-cell configuration of the patch-clamp technique. Shifts in the reversal potential of the current induced by replacement of external Cl− with foreign anions, gave the following selectivity sequence based on permeability ratios (P x/P Cl): SCN−>I−>NO 3 − >Br−>Cl−>F−>aspartate>glutamate. Using a continuum electrostatic model we calculated that this lyotropic sequence resulted from the interaction between anions and a polarizable tunnel with an effective dielectric constant of ∼23. Our data revealed that anions with P x/PCl > 1 accelerated activation kinetics in a voltage-independent manner and slowed deactivation kinetics. Moreover, permeant anions enhanced whole-cell conductance (g, an index of the apparent open probability) in a voltage-dependent manner, and shifted leftward the membrane potential-g curves. All of these effects were produced by the anions with an effectiveness that followed the selectivity sequence. To explain the effects of permeant anions on activation kinetics and g Cl we propose that there are 2 different anion-binding sites in the channel. One site is located outside the electrical field and controls channel activation kinetics, while a second site is located within the pore and controls whole-cell conductance. Thus, interactions of permeant anions with these two sites hinder the closing mechanism and stabilize the channel in the open state.

Journal

The Journal of Membrane BiologySpringer Journals

Published: Jan 1, 2004

References

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