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Electron microscope radioautographic study of glycogen synthesis in the rabbit retina
Abstract:
Glycogen is present in the rabbit retina in monoparticulate form. Beta particles ( approximately 229 A) are abundant in Müller cell cytoplasm, particularly in its inner portion, decreasing in number outwards along the cell. They are slightly larger ( approximately 250 A) and much scarcer in neurons, though regularly present in the juxtanuclear Golgi region of ganglion cells. When the retina was incubated in a glucose-free medium, it was rapidly depleted of native glycogen. On further incubation in medium containing glucose-(3)H plus unlabeled glucose, glycogen reappeared in the form of beta particles of the same size and distribution as native ones, while radioautography revealed the appearance of amylase-labile radioactivity in the same locations. This newly formed glycogen was not associated with any particular organelle. The rate of synthesis, as judged from the amount of radioactivity, was high in the inner portion of Müller cells and declined uniformly toward the cell outer end, following a logarithmic gradient. The rate of synthesis was low in ganglion cells, at best approaching values in the outer portion of Müller cells. The concentration of glycogen in the inner portion of Müller cells is consistent with the view that it may be the source of glucose for the anaerobic glycolysis prevailing in the inner retina.
Insights
Rabbit retina glycogen synthesis occurs in Müller cells and ganglion cells. Müller cells, particularly their inner portions, show high glycogen synthesis rates, suggesting a glucose source for inner retina glycolysis.
Area of Science:
- Ophthalmology
- Cell Biology
- Neuroscience
Background:
- Glycogen, a glucose polymer, serves as an energy reserve in various tissues.
- The distribution and synthesis of glycogen in the rabbit retina are not fully understood.
Purpose of the Study:
- To investigate the localization and synthesis of glycogen in the rabbit retina.
- To determine the role of Müller cells and ganglion cells in retinal glycogen metabolism.
Main Methods:
- Incubation of rabbit retinal tissue in glucose-free and glucose-supplemented media.
- Radioautography to detect radiolabeled glucose incorporation into glycogen.
- Electron microscopy to visualize glycogen particle morphology and distribution.
Main Results:
- Native glycogen in rabbit retina exists as beta particles (approx. 229 Å) in Müller cells and ganglion cells.
- Retinal glycogen was depleted in glucose-free medium and resynthesized upon glucose reintroduction.
- Newly synthesized glycogen appeared as beta particles, with synthesis rates highest in the inner Müller cell cytoplasm and low in ganglion cells.
- Glycogen synthesis followed a logarithmic gradient along Müller cells, suggesting localized metabolic activity.
Conclusions:
- Müller cells, especially their inner portions, are primary sites of glycogen synthesis in the rabbit retina.
- The high concentration and synthesis rate of glycogen in inner Müller cells support its role as a glucose source for anaerobic glycolysis in the inner retina.