Metabolic and Anatomical Specialization Within the Retina

Lolley, Richard N.

doi:10.1007/978-1-4615-7157-5_20

Cited by 1 publication

(5 citation statements)

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“…The gluconeogenic pathway is difficult to quantify accurately in an intact piece of tissue such as the retina that (1) has the highest metabolic rate (Lolley, 1969;Graymore, 1970), (2) relies solely on glucose as its energy source (Lolley, 1969;Graymore, 1970) and (3) does not release detectable amounts of glucose to the incubation medium. The methodology used in the present study defines the gluconeogenic pathway empirically by assuming that retinal glycogen acts as a 'trap' for the glucose derived metabolically from ["4C]glutamate or lactate.…”

Section: Discussionmentioning

confidence: 99%

“…In order to recycle lactate, there must be a reversible lactate dehydrogenase isoenzyme. Retinal lactate dehydrogenase activity is high (Lolley, 1969;Graymore, 1970), and histochemically the enzyme has been localized in large part to the Muller (glial) cell . Histochemically, the lactate dehydrogenase reaction must be driven in the direction of pyruvate (Pearse, 1972), which may suggest that the Muller cell contains this particular lactate dehydrogenase isoenzyme.…”

Section: Discussionmentioning

confidence: 99%

“…In brief, to determine the activity of the gluconeogenic pathway in liver and kidney, the release of glucose from the tissue incubated in a glucose-free medium is measured or an increase in hepatic glycogen is measured. This particular approach could not be used for the retina, since the retina relies solely on glucose as its energy source (Lolley, 1969;Graymore, 1970) and does not release detectable amounts of glucose to the incubation medium (S. S. Goldman, unpublished work). Therefore it was assumed that retinal glycogen can act as a 'trap' for the glucose derived metabolically from the '4C-labelled non-carbohydrate precursors, as described previously (Goldman & Witkovsky, 1987).…”

Section: Rationale For Determination Of the Gluconeogenic Pathwaymentioning

confidence: 99%

Section: Relationship Between Gluconeogenesis and Energy Metabolismmentioning

confidence: 99%

“…Since the retina produces prodigious amounts of lactate aerobically (Lolley, 1969;Graymore, 1970), the rate of its production has been used to monitor energy metabolism (Winkler, 1981). However, the high aerobic glycolytic capacity of the retina has been observed only in vitro (Lolley, 1969;Graymore, 1970) and its capacity in vivo still remains uncertain (Tornquist & Alm, 1979). In the presence of millimolar concentrations of lactate, which mimic the conditions in vivo (Matschinsky et al, 1968;Lolley, 1972;Lolley & Schmidt, 1974), lactate production is extinguished completely, or at least is suppressed to undetectable values (Tables 2 and 4).…”

Section: Relationship Between Gluconeogenesis and Energy Metabolismmentioning

confidence: 99%

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Gluconeogenesis in the amphibian retina. Lactate is preferred to glutamate as the gluconeogenic precursor

Goldman

1988

Biochemical Journal

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The capacity for gluconeogenesis in the isolated amphibian retina was found to be approx. 70-fold greater with lactate than with glutamate as the gluconeogenic precursor, 1426 versus 21 pmol of glucose incorporated into glycogen/h per mg of protein. It was also found that 11-15% of the glucosyl units in glycogen are derived from C3 metabolites of the glycolytic pathway, suggesting that lactate is recycled within the retina. In concert with these metabolic observations, a full complement of the gluconeogenic enzymes was detected in retinal homogenates. These included: glucose-6-phosphatase, fructose-1,6-bisphosphatase, acetyl-CoA-dependent pyruvate carboxylase and phosphoenolpyruvate carboxykinase. Agents that regulate the rate of gluconeogenesis in hepatic tissue were tested on the retina. At concentrations of glutamate and lactate that are presumed to be relevant physiologically, it was found that vasoactive intestinal peptide, ionophore A23187 and elevated [K+] each enhanced the rate of gluconeogenesis in Ringer containing 50 microM-glutamate, whereas in Ringer containing 8.5 mM-lactate these agents inhibited the rate of gluconeogenesis. Further, it was found that the classic gluconeogenic hormone glucagon inhibited gluconeogenesis in both glutamate- and lactate-containing Ringer. Retinal energy metabolism was found to be altered in lactate-containing Ringer, in that lactate production was suppressed completely. In addition, glycogen metabolism appeared to be dependent on increased cytosolic Ca2+ and was insensitive to increased retinal cyclic AMP.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%