Effect of hypoxemia and hyperglycemia on pH in the intact cat retina

Objective: To examine the effects of acute hypoxemia and hyperglycemia on retinal pH to understand hyperglycemia-induced changes in the normal intact cat retina. Methods: Spatial profiles of extracellular hydrogen ion (H ⁺) concentration were obtained from the cat retina, in vivo, using pH-sensitive microelectrodes during normoxia (arterial partial pressure of oxygen [PaO ₂]=114.5±7.9 mm Hg), normoglycemia (plasma glucose concentration, 117±19 mg/dL), acute hypoxemia (PaO ₂=29. 5±2.2 mm Hg), and acute hyperglycemia (plasma glucose concentration, 303±67 mg/dL). An H ⁺ diffusion model was fitted to the outer retinal data to quantify photoreceptor H ⁺ production. The inner retinal pH was also examined. Results: Hypoxemia induced a mean acute panretinal acidification of 0.16 pH units that originated from a 2.55-fold increase in net photoreceptor H ⁺ production. Hyperglycemia induced an acute panretinal acidification of 0.12 pH units; however, photoreceptor H ⁺ production levels remained unchanged. Retinal pH changes followed the course of arterial PaO ₂ and blood glucose changes. Conclusions: The increase in photoreceptor H ⁺ production during hypoxemia confirms the importance of glycolysis in the retina. Hyperglycemia-induced pH changes resulted from either increased inner retinal H ⁺ production or decreased H ⁺ clearance/neutralization. Clinical Relevance: The hyperglcemia-induced acidification that originates in the inner retina suggests that retinal acidosis may contribute to the development of diabetic retinal disease.