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. 1989 May 5;244(4904):578-80.
doi: 10.1126/science.2785716.

Spatial buffering of light-evoked potassium increases by retinal Müller (glial) cells

C J Karwoski  1 , H K Lu, E A Newman
Affiliations

Spatial buffering of light-evoked potassium increases by retinal Müller (glial) cells

C J Karwoski et al. Science. .

Abstract

Activity-dependent variations in extracellular potassium concentration in the central nervous system may be regulated, in part, by potassium spatial buffering currents in glial cells. The role of spatial buffering in the retina was assessed by measuring light-evoked potassium changes in amphibian eyecups. The amplitude of potassium increases in the vitreous humor was reduced to approximately 10 percent by 50 micromolar barium, while potassium increases in the inner plexiform layer were largely unchanged. The decrease in the vitreal potassium response was accurately simulated with a numerical model of potassium current flow through Müller cells, the principal glial cells of the retina. Barium also substantially increased the input resistance of Müller cells and blocked the Müller cell-generated M-wave, indicating that barium blocks the potassium channels of Müller cells. Thus, after a light-evoked potassium increase within the retina, there is a substantial transfer of potassium from the retina to the vitreous humor by potassium current flow through Müller cells.

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Figures

Fig. 1
Fig. 1
Light-evoked [K+]o changes in the vitreous humor and in the IPL (A) before, (B) approximately 5 min after Ba2+ application (50 μM), and (C) approximately 1 hour after washout of a frog eyecup. The secondary peak in the IPL at light off is the delayed off response (20). Light stimulus (diffuse illumination; intensity, 3.2 lux) is indicated at the bottom. Here and in Fig. 2 the ordinate represents the linear K+ concentration. Resting [K+]o in the IPL, 2.7 mM.
Fig. 2
Fig. 2
The [K+]o response and the intraretinal ERG (negative upward) recorded simultaneously in the IPL of frog (A) before, (B) approximately 5 min after Ba2+ application (50 μM), and (C) approximately 1 hour after washout. The PNR and the increase in [K+]o were largely unaffected by Ba2+, while the M-wave was greatly reduced. Stimulus, 0.3-mm spot; intensity, 3.2 lux.
Fig. 3
Fig. 3
Computer simulation of the experiment in Fig. 1, A and B. Simulated Ba2+ in the model (i) substantially reduced and slowed the [K+]o increase in the vitreous and (ii) slowed the decay of the [K+]o response in the IPL (18).
See this image and copyright information in PMC

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