Experimental evidence is presented which shows that the predominant energy-yielding metabolic pathway in the Muller cell of the vertebrate retina is glycolysis. Some important roles of the Muller cell are to maintain ion constancy of the extracellular space, sequester neurotransmitters, detoxify NH3 and probably to provide sustenance to surrounding neurons. The goal of this grant is to define which metabolic pathway (glycolytic or oxidative) supports these different Muller cell functions. Bulk isolated Muller cells prepared from bullfrog retina will be employed in these studies. Transport dependent metabolism (lactate production and/or O2 consumption) will be used to determine which metabolic pathway supports ion transport. Cells will be incubated in the absence and presence of ouabain to determine these metabolic parameters. The two metabolic pathways will be isolated with the use of metabolic inhibitors: N2, iodoacetate and antimycin A. The metabolic pathway which supports glutamine synthesis will be addressed as well as the cell (Muller or neuron) that supplies the glutamate. To assess whether Muller cells provide sustenance to surrounding neurons, the mobilization of Muller cell glycogen will be studied. Muller cell glycogen will be labeled with 3H-glucose and the rate of loss of label from glycogen will be followed by challenging the cells with VIP, biogenic amines or K+. The cAMP levels will be measured to determine if increases in cAMP account for the conversion of phosphorylase b to its active """"""""a-form."""""""" Other studies will determine the cellular site(s) for gluconeogenesis, i.e., the conversion of 3H-glutamate to glucose and its incorporation into glycogen as well as the fixation of CO2, i.e., the incorporation of 14C-HCO3 into TCA cycle intermediates and into amino acids. If the Muller cell is found to be the site for gluconeogenesis, then this pathway will be further characterized with respect to the conversion of amino acids into glucose and lactate as well as glycogen and the possibility that GABA may be converted to carbohydrate. The long-term objectives are to broaden our understanding of how the metabolism of the Muller cell supports retinal function. A disturbance within the metabolic framework of the Muller cell caused by a genetic defect or a vascular accident may conceivably underlie the pathophysiologic process that results in certain inherited retinal degenerative disorders or to the loss of vision precipitated by other events.
| Goldman, S S (1990) Evidence that the gluconeogenic pathway is confined to an enriched Muller cell fraction derived from the amphibian retina. Exp Eye Res 50:213-8 |
| Goldman, S S (1988) Gluconeogenesis in the amphibian retina. Lactate is preferred to glutamate as the gluconeogenic precursor. Biochem J 254:359-65 |
| Goldman, S S; Witkovsky, P (1987) Evidence for gluconeogenesis in the amphibian retina. Exp Eye Res 44:65-71 |
