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The role of potassium conductance in the generation of light responses in Müller cells of the turtle retina

Published online by Cambridge University Press:  01 March 1998

DAVID M. LINN
Affiliation:
Department of Ophthalmology, John A. Moran Eye Center, University of Utah, Salt Lake City Present address: LSU Eye Center, 2020 Gravier St. Suite B, New Orleans, LA 70112, USA.
EDUARDO SOLESSIO
Affiliation:
Department of Ophthalmology, John A. Moran Eye Center, University of Utah, Salt Lake City
IDO PERLMAN
Affiliation:
Department of Ophthalmology, John A. Moran Eye Center, University of Utah, Salt Lake City The Bruce Rappaport Faculty of Medicine, Technion and the Rappaport Institute, Haifa, Israel.
ERIC M. LASATER
Affiliation:
Department of Ophthalmology, John A. Moran Eye Center, University of Utah, Salt Lake City

Abstract

Müller cells are highly permeable to potassium ions and play a major role in maintaining potassium homeostasis in the vertebrate retina during light-evoked neuronal activity. Potassium fluxes across the Müller cell's membrane are believed to underlie the light-evoked responses of these cells. We studied the potassium currents of turtle Müller cells in the retinal slice and in dissociated cell preparations and their role in the genesis of the light-evoked responses of these cells. In either preparation, the IV curve, measured under voltage-clamp conditions, consisted of inward and outward currents. A mixture of cesium ions, TEA, and 4-AP blocked the inward current but had no effect on the outward current. Extracellular cesium ions alone blocked the inward current but exerted no effect on the photoresponses. Extracellular barium ions blocked both inward and outward currents, induced substantial depolarization, and augmented the light-evoked responses, especially the OFF component. Exposing isolated Müller cells to a high potassium concentration did not cause any current or voltage responses when barium ions were present. In contrast, application of glutamate in the presence of barium ions induced a small inward current that was associated with a substantially augmented depolarizing wave relative to that observed under control conditions. This observation suggests a role for an electrogenic glutamate transporter in generating the OFF component of the turtle Müller cell photoresponse.

Type
Research Article
Copyright
1998 Cambridge University Press

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