Preretinal pH changes in the rabbit under conditions of light and dark

Preretinal pH was measured in the avascular region of 19 rabbit retinas during alternating cycles of light and dark, using a miniature, needle-type pH electrode. In 14 experiments with the rabbits breathing room air, cyclic changes in pH, decreasing in the dark and increasing in the light, were observed. The transition from light to dark caused a mean pH decrease of 0.047 +/- 0.029 U (n = 14). An inversion of the light/dark pH response was observed in five experiments. In three of these, the effect was induced by having the rabbits breathe 100% O2. In the five rabbits showing a reversed response, a mean pH increase of 0.034 +/- 0.025 pH U was observed in the dark; light-ON caused a decrease of 0.035 +/- 0.025 pH U. The direction of the preretinal pH change is thought to be the net effect of light/dark-induced changes in the metabolism of the photoreceptors and inner retinal layers (defined for the purpose of this paper as the region between the outer synaptic layer and the inner limiting membrane). In six separate experiments, retinal metabolism was assessed by measuring preretinal PO2 during alternating cycles of light and dark while the rabbits breathed room air. Oxygen tension declined from a mean of 14.5 +/- 6.2 (S.D.) mmHg in the light to 10.1 +/- 5.4 (S.D.) mmHg in darkness, and increased from a mean of 10.9 +/- 5.1 (S.D.) mmHg in darkness to 15.4 +/- 5.8 (S.D.) mmHg in the light. The time courses of the pH and the PO2 changes were similar.(ABSTRACT TRUNCATED AT 250 WORDS)