Purchase this article with an account.
K.F. LaNoue, D.A. Berkich, Y. Xu; The Effect of Light on Glutamate Metabolism in the Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5153.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: Synaptic transmission in the retina is more rapid in the dark than in the light. Recently Leith et al. (J Neurochem 2001, 76, 1712) developed techniques for measuring glutamate and glutamine fluxes in isolated excised rat retina. Since glutamatergic neural activity increases in the dark, it was of interest to see if increases in flux through the glutamine glutamate cycle could be observed correlating with increased neural activity. Methods: Male Sprague Dawley rats were dark- or light-adapted. Their retinas were removed under anesthesia in room light or dim red light. Bicarbonate in the medium was labeled with carbon 14 and incubations were allowed to proceed in the dark or light for 20 min. to achieve steady state labeling of glutamate, glutamine, and aspartate via pyruvate carboxylase. Retinas were then placed in identical medium without carbon 14. Retinas were removed from the medium at times varying from 0 to 16 minutes. Analysis of washout kinetics of glutamate, glutamine and aspartate permit calculation of neuronal glutamate turnover, Muller cell aspartate turnover, and glutaminase flux. Results: The first order rate constant of glutamate metabolism (kA) could be determined from the first order decline of glutamate specific activity during the "washout" phase of the experiment. Glutamate specific activity and kA were both higher in the dark-adapted rat retinas that had not been exposed to light during surgery or during incubations. The average kA of "dark" retinas was 0.103±0.007 min-1 and of "light" retinas was 0.069±0.006 min-1. From these values and from the specific activities of glutamine at t=0, it is possible to determine flux through the glutamine glutamate cycle. These values were 1.29±0.09 nmoles/min x mg. retinal protein for dark retinas and 0.74 nmoles min. mg. for "light" retinas. The data also indicate rates of entry of 14C from bicarbonate was 70% faster in dark retinas. Conclusion: It is possible to quantitatively assess the changes in glutamate metabolism neurotransmission in the dark. An increase in Muller cell anaplerotic synthesis of the glutamate appears to be an integral part of the metabolic change.
This PDF is available to Subscribers Only