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Primate rod and cone photoreceptors may differ in glucose accessibility
M Nihira1, K Anderson, F A Gorin
1Department of Ophthalmology, University of California School of Medicine, Davis 95816, USA.
Investigative Ophthalmology & Visual Science
|June 1, 1995
Summary
Retinal cones can transport glucose and use internal glycogen stores, unlike rods. This suggests cones may better tolerate low glucose but risk acid damage during hypoxia.
Area of Science:
- Ophthalmology
- Neuroscience
- Cell Biology
Background:
- Glucose is vital for retinal cells, including photoreceptors.
- Retinal glucose supply comes from circulation and internal glycogen breakdown.
- Glucose deprivation is a key factor in retinal ischemia.
Purpose of the Study:
- To identify where glucose enters the retina.
- To determine where glucose is generated within the retina.
- To investigate the roles of glucose transporters and glycogen phosphorylase in retinal glucose metabolism.
Main Methods:
- Immunohistochemistry was used to localize glucose transporter 1 (GluT-1) and glycogen phosphorylase (GlyP) isozymes.
- Adult human and monkey retinas were analyzed.
- Ultrastructural analysis examined glucose transporter localization in photoreceptor segments.
Main Results:
- Brain glycogen phosphorylase (B-GlyP) was found in cone photoreceptors, not rods.
- Muscle glycogen phosphorylase (M-GlyP) was localized to specific inner plexiform layers in monkey retinas.
- GluT-1 staining was widespread, including retinal vasculature, RPE, and photoreceptor segments.
Conclusions:
- Both rod and cone photoreceptors can transport exogenous glucose.
- Only cone photoreceptors possess the capacity for endogenous glucose generation via glycogenolysis.
- Cones may be more resilient to hypoglycemia but susceptible to acidotic damage during hypoxia due to lactic acid buildup.