Glucose metabolism in pig outer retina in light and darkness

Abstract

In the pig eye, oxygen and glucose consumption in the outer retina are reduced in light compared to the consumption in the dark and most of the glucose consumed is metabolized to lactate both in light and in the dark. In the present study, in order to characterize the metabolism of glucose in the inner retina. Blood was collected from an artery and from a plexus on the optic nerve draining blood from the retina. Arteriovenous concentration differences for glucose, lactate and oxygen were determined. Observations were made in dark-adapted eyes and then after light adaptation. The consumption of oxygen and glucose and the lactate formation in the inner retina were calculated on the basis of these observations and recent data for retinal blood flow. In dark-adapted eyes, approx. 69% of the glucose was oxidized and approx. 20% was used in lactate formation. After 5-10 min of exposure to constant light, the levels of oxygen consumption and lactate formation were no different from those in darkness. The results indicate that lactate formation is a normal property of the pig inner retina, but that it is much less pronounced than in the outer part. The metabolism of the inner retina in constant light is similar to that in darkness. A comparison with data for the outer retina indicates that oxygen consumption in the inner retina in constant light is approx. 47% of that in the whole retina, while for glucose consumption and lactate production, the corresponding figures are approx. 12 and 8%, respectively.

Pyruvate kinase and aspartate-glutamate carrier distributions reveal key metabolic links between neurons and glia in retina

“…Our findings that MCs do not express PK and that PRs express abundant PKM2 suggested that PRs, and not MCs, are the primary source of Lac. Retinas convert Glc to Lac at a very fast rate (4)(5)(6)(7)13 deficiency causes PR degeneration (27), so we extracted metabolites from mutant and control retinas and quantified them by GC/MS (Fig. S4).…”

“…Aerobic glycolysis accounts for 80-96% of Glc used by retinas (4)(5)(6)(7). Retinas are made up of neurons and glia (8).…”

Carbonic anhydrase XIV is enriched in specific membrane domains of retinal pigment epithelium, Müller cells, and astrocytes

“…Of the intracellular isoforms, CA V is expressed in neuronal and glial mitochondria (10), and CA II is highly expressed in oligodendrocytes and in Müller cells in retina (9,15). Of the membrane-bound isoforms in brain, CA IV has been demonstrated on the luminal surface of cortical capillary endothelial cells (16,17) and on neurons and glia in selected regions of brain (18), and CA XIV has been found on neurons and axons in brain tissue (11). Thus, the CA XIV isoform may also be of importance for regulation of neuronal excitability and transport processes in brain.…”

“…Moreover, the direction of transport is better defined in the retina than in the more complex neuropil of the brain. For example, the flux of lactate has been shown to occur constitutively from the inner to the outer aspect of the retina (18). Other transport processes may shift polarity depending on the metabolic activity.…”

Impaired dark adaptation in polycythemia. Improvement after treatment

“…Although dark adaptation is a complex psychovisual function, the most probable reason for this is the high energy demand of the photoreceptor complex, which for proper function is critically dependent upon the oxygen tension in the outer segment of the retina, as shown in animal experiments (Bill & Sperber 1990;Linsenmaier & Braun 1992;Braun et al 1995;Wang et al 1997). As dark adaptometry is a rather simple psychovisual test, far less complicated than ordinary psychometric tests, we chose this sensitive function to study the consequenses of a possibly insufficient microcirculation secondary to polycythemia.…”