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Science 5 May 1989:
Vol. 244. no. 4904, pp. 578 - 580
DOI: 10.1126/science.2785716
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Articles

Science, Vol 244, Issue 4904, 578-580
Copyright © 1989 by American Association for the Advancement of Science

articles

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

CJ Karwoski, HK Lu, and EA Newman

Department of Psychology, University of Georgia, Athens 30602.

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 Muller cells, the principal glial cells of the retina. Barium also substantially increased the input resistance of Muller cells and blocked the Muller cell-generated M-wave, indicating that barium blocks the potassium channels of Muller 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 Muller cells.


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