Changes in [K+]0 at the vitreal surface compared with those around receptors in the isolated rabbit retina

Isolated rabbit retinas were superfused from the receptor side with a plasma-saline mixture kept at 35 degrees C. The vitreal side was exposed to an atmosphere of humidified warm oxygen. In one study the second-order neuronal activity was suppressed with aspartate and glutamate; in another study transmission was not blocked. When all neurons were active, [K+]0 around receptors was 4.5 +/- 0.4 mM in the dark. During a long (60s) exposure to light stimulus, [K+]0 dropped to 73% of the dark value and reaccumulated to 80%. At the vitreal surface, [K+]0 in the dark was 4.7 +/- 0.8 mM. During the 60s light stimulus, [K+]0 increased transiently, dropped to 83% of the dark value, then increased again to 91%. A continuous decrease of [K+]0 at the vitreal surface during long light stimuli concurrent with the increase of [K+]0 around receptors would indicate that the spatial buffering capability of the Müller cells contributes to the reaccumulation of potassium. Such a decrease, however, was not detected. After the blockage of transmission, [K+]0 values did not vary significantly from those after light stimulus in unblocked preparations. In the dark, [K+]0 was 5.2 +/- 0.9 mM at the vitreal surface and 4.6 +/- 0.4 mM around the receptors.