Glucose metabolism in freshly isolated mammalian Müller glial cells

Glucose metabolism in freshly isolated mammalian Müller glial cells

X ICER Abstracts Tuesday, Sep 22, 1992 La Palms/B 212 4 CARBOHYDRATE METABOLISM IN RETINAL GLIAL CELLS Tsacoooulos. M. Experimental Ophthalmology La...

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X ICER Abstracts

Tuesday, Sep 22, 1992 La Palms/B 212

4 CARBOHYDRATE METABOLISM IN RETINAL GLIAL CELLS Tsacoooulos. M. Experimental Ophthalmology Laboratory, University of Geneva, Switzerland

In the retina of the honeybee drone gliel cells and photorecepkx-c& constitute two distinct metabolic compartments. The phosphorylation of glucose and its subsequent incorporation into glycogen occur essentially in glia, whereas 02 consumption occurs in the DhOtOreCeDtOrs. After 3H-nlucose loadinn of SuDerfused retinal slices. ght sti&lation of the ihotoreceptors-induce2 a significant rise in Siye light stimulation induces H-glycogen turnover in the glia. about a 47% rise In the form tion of H-2DG-6P in glial cells, the J increase of the availability of H-glycosyls thaf are incorporated into glycogen accounts for the effect of light on H-glycogen. Repetitive light stimulation of the retina induced about 400% rise of consumption in the photoreceptors but only 30% increase of PI-y!! production. Apparently, the transferred substrate from glial cells t8 the photoreceptors is neither p{i uvate nor lactate. When the retina is incubated in Ringer carrying C(U)-glucose, more than 50% of the incorporated radioactivity was found in the amino acid alanine. The other labelled amino acids were glutamate, glutamine and aspartate. Proline and taurine were hiehlv concentrated in the retina (60 and 30 mM) but were not labelled.-L&ge amounts of labelled and .&labelled alanine were found in the extracellular space of the retina. glycolytic inhibitor iodoacetate supresses the formation of JheCalanine and the light-induced increase of QO, in the photoreceptors. Under physiological conditionsldepetitive light stimulation induced a C-glutamate, formed after 60 min C(U)-glucose because it accelerates the Krebs cycle leading to a faster consumption of glutamate and the formation of excess of NH3 which transitorily alkanizes the extracellular space.

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5 GLUCOSE METABOLISM GLIAL CELLS Poitrv-hm8tiC.L.. Expsrimental Ophlhal&logy

IN FRESHLY Lab. Uniz

ISOLATED of Geneva M&

MAMMALIAN

MiiLLER

Sch, Switzerland

The metabolism of glucose through the glycolytic pathway is vital to maintaining normal retinal function in manmxds. An important metabolic function of Miil1e.f glial cells in sifa is ghwse up&s and phospbotylation. We am exploring the metabolism of glucose through the glycolytic pathway and the Krebs cycle in different retinal cell types, but particularly in MGller cells. because gh~cosederivcd mstabolites that they release may subserve enerm tads for the function of other cells in the retina. For this resson~ Miiller cells w&z freshly isolated from the guinea pig retina, enriched by Percoll centri~gstion. and Uwir metsbolic activiiy t&cd. Their incubation in the ~mettcc of II-2dmxvelucosc rcvcnlod chat tbev contained sufiicicnt ATP to &nsively phosphoryl&” 3H-2-deoxy&cose to 31i-2-aeoxyglucose-6-phosphate. a

were difffyt from one ccl1 type to tic other. If both Mi#r cells and photoreceptors released C-lactste. Milller cells released 4 different C-mstabolites which were not detected intracellularly. In contrss& of the 4 major “C-nxtabolites released by phofvtors. 3 wen, found intracelhdarly. One of these metabolites was identified BS C-glutamate. These findings suggest a possible metabolic interaction betwcen Milller cells snd photorecqxors by which glucose-derived metabolitcs rclessed by Milller cells are transfer& for transformation by photoreceptors. This would bs important for replenishing photoreceptor transmitter pools of glutamate which may be limited.

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