Nuclear magnetic resonance and biochemical measurements of glucose utilization in the cone-dominant ground squirrel retina.
OBJECTIVE
To provide quantitative information on glucose utilization in cone-dominant ground squirrel retinas.


METHODS
Ground squirrel eyecups were incubated in medium containing (14)C-glucose, and the production of (14)CO(2) was measured. Measurements were also made of lactic acid production (glycolysis). Nuclear magnetic resonance (NMR) was used to track metabolites generated from (13)C-1 glucose.


RESULTS
Ground squirrel eyecups produced lactate at a high rate and exhibited normal histology. Light-adaptation reduced glycolysis by 20%. Ouabain decreased glycolysis by 25% and decreased (14)CO(2) production by 60%. Blockade of glutamate receptors had little effect on the glycolysis and (14)CO(2) produced. When metabolic responses were restricted to photoreceptors, light caused a 33% decrease in (14)CO(2) production. The rate of (14)CO(2) production was less than 10% of lactate production. Lactate was the major product formed from (13)C-glucose. Other (13)C-labeled compounds included glutamate, aspartate, glutamine, alanine, taurine, and GABA. Lactate was the only product detected in the medium bathing the ground squirrel retinas. The rod-dominant rat retina exhibited a similar pattern of metabolites formed from glucose.


CONCLUSIONS
Lactate, not CO(2), is the major product of glucose metabolism in both ground squirrel and rat retinas. Active Na(+) transport, however, depends more on ATP produced by mitochondria than by glycolysis. A relatively high fraction of ATP production from glycolysis and glucose oxidation continues in the absence of active Na(+) pumping and glutamatergic transmission. Major neurotransmitters are synthesized from the aerobic metabolism of glucose; anoxia-induced impairment in retinal synaptic transmission may be due to depletion of neurotransmitters.
Winkler
Barry S
BS
Eye Research Institute, Oakland University, Rochester, Michigan 48309, USA. winkler@oakland.edu
Starnes
Catherine A
CA
Twardy
Brandon S
BS
Brault
Diane
D
Taylor
R Craig
RC
D000818:Animals; D000968:Antimycin A / Q000494:pharmacology; D002245:Carbon Dioxide / Q000378:metabolism; D004579:Electron Transport / Q000187:drug effects; D004734:Energy Metabolism / Q000502:physiology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism*; D006019:Glycolysis / Q000502:physiology; D019344:Lactic Acid / Q000378:metabolism; D008027:Light; D009682:Magnetic Resonance Spectroscopy; D010042:Ouabain / Q000633:toxicity; D051381:Rats; D017207:Rats, Sprague-Dawley; D017470:Receptors, Glutamate / Q000378:metabolism; D012160:Retina / Q000378:metabolism* / Q000528:radiation effects; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism* / Q000528:radiation effects; D012589:Sciuridae
D018691:Excitatory Amino Acid Antagonists; D017470:Receptors, Glutamate; D002245:Carbon Dioxide; D019344:Lactic Acid; D010042:Ouabain; D000968:Antimycin A; D005947:Glucose