Metabolic Responses to Light in Monkey Photoreceptors

Autor: Robert A. Linsenmeier, Ewa Budzynski, Robert Flynn, Gülnur Birol, Shufan Wang
Rok vydání: 2010
Předmět:
Zdroj: Current Eye Research. 35:510-518
ISSN: 1460-2202
0271-3683
DOI: 10.3109/02713681003597255
Popis: Purpose: Transient changes in intraretinal oxygen tension (PO 2 ) in response to light stimuli were studied in order to understand the dynamics of light-evoked changes in photoreceptor oxidative metabolism. Methods: PO 2 changes during illumination were recorded by double-barreled microelectrodes in the outer part of the perifoveal retina in five macaques (Rhesus and Cynomolgus) and were fitted to a single exponential equation to obtain the time constant (τ) and maximum PO 2 change. Results: At the onset of light, PO 2 increased at all illuminations in all animals. The magnitude of the light-evoked PO 2 change increased with increasing illumination over 3–4 log units but decreased in all animals at the maximum illumination. The median time constant of the PO 2 change (τ ) was 26 sec and was not correlated with illumination. The time constant for the return to darkness was similar for illuminations below rod saturation. Since O 2 diffusion is fast over the short distance from the choroid to the inner segments, τ reflects the time course of the underlying change in oxidative metabolism. Conclusions: Previous results suggested that two competing processes influence the change in photoreceptor oxidative metabolism with light, Na + /K + pumping and cyclic guanosine monophosphate (cGMP) turnover. Because a single exponential fitted the PO 2 data, it appears that these processes have time constants that differ by no more than a few seconds in primate. In monkeys, τ is longer than previously reported values for cat and rat. Longer time constants are related to larger photoreceptor volume, possibly because metabolic rate is controlled by intracellular Na + , and a change in intracellular Na + after the onset of illumination occurs more slowly in larger photoreceptors. The “metabolic threshold” illumination that reduced oxygen consumption by about 10% is approximately the same as the illumination that closes 10% of the light-dependent cation channels that are open in the dark. keyw ORDS: Non-human primate; Monkey; Retinal metabolism; Photoreceptor; Retina; Oxygen; Macaque
Databáze: OpenAIRE
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