Mouse retinal pigment epithelial cells exhibit a thiocyanate-selective conductance

Mouse retinal pigment epithelial cells exhibit a thiocyanate-selective conductance The basolateral membrane anion conductance of the retinal pigment epithelium (RPE) is a key component of the transepithelial Cl− transport pathway. Although multiple Cl− channels have been found to be expressed in the RPE, the components of the resting Cl− conductance have not been identified. In this study, we used the patch-clamp method to characterize the ion selectivity of the anion conductance in isolated mouse RPE cells and in excised patches of RPE basolateral and apical membranes. Relative permeabilities (PA/PCl) calculated from reversal potentials measured in intact cells under bi-ionic conditions were as follows: SCN− >> ClO4− > NO3− > I− > Br− > Cl− >> gluconate. Relative conductances (GA/GCl) followed a similar trend of SCN− >> ClO4− > NO3− > I− > Br− ≈Cl− >> gluconate. Whole cell currents were highly time-dependent in 10 mM external SCN−, reflecting collapse of the electrochemical potential gradient due to SCN− accumulation or depletion intracellularly. When the membrane potential was held at −120 mV to minimize SCN− accumulation in cells exposed to 10 mM SCN−, the instantaneous current reversed at −90 mV, revealing that PSCN/PCl is approximately 500. Macroscopic current recordings from outside-out patches demonstrated that both the basolateral and apical membranes exhibit SCN− conductances, with the basolateral membrane having a larger SCN− current density and higher relative permeability for SCN−. Our results suggest that the RPE basolateral and apical membranes contain previously unappreciated anion channels or electrogenic transporters that may mediate the transmembrane fluxes of SCN− and Cl−. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png AJP - Cell Physiology The American Physiological Society

Mouse retinal pigment epithelial cells exhibit a thiocyanate-selective conductance

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ISSN
0363-6143
eISSN
1522-1563
D.O.I.
10.1152/ajpcell.00231.2017
Publisher site
See Article on Publisher Site

Abstract

The basolateral membrane anion conductance of the retinal pigment epithelium (RPE) is a key component of the transepithelial Cl− transport pathway. Although multiple Cl− channels have been found to be expressed in the RPE, the components of the resting Cl− conductance have not been identified. In this study, we used the patch-clamp method to characterize the ion selectivity of the anion conductance in isolated mouse RPE cells and in excised patches of RPE basolateral and apical membranes. Relative permeabilities (PA/PCl) calculated from reversal potentials measured in intact cells under bi-ionic conditions were as follows: SCN− >> ClO4− > NO3− > I− > Br− > Cl− >> gluconate. Relative conductances (GA/GCl) followed a similar trend of SCN− >> ClO4− > NO3− > I− > Br− ≈Cl− >> gluconate. Whole cell currents were highly time-dependent in 10 mM external SCN−, reflecting collapse of the electrochemical potential gradient due to SCN− accumulation or depletion intracellularly. When the membrane potential was held at −120 mV to minimize SCN− accumulation in cells exposed to 10 mM SCN−, the instantaneous current reversed at −90 mV, revealing that PSCN/PCl is approximately 500. Macroscopic current recordings from outside-out patches demonstrated that both the basolateral and apical membranes exhibit SCN− conductances, with the basolateral membrane having a larger SCN− current density and higher relative permeability for SCN−. Our results suggest that the RPE basolateral and apical membranes contain previously unappreciated anion channels or electrogenic transporters that may mediate the transmembrane fluxes of SCN− and Cl−.

Journal

AJP - Cell PhysiologyThe American Physiological Society

Published: Oct 1, 2018

References

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