Purchase this article with an account.
A. Chertov, M. Gilbert, I. R. Sweet, J. B. Hurley; The Effects of Calcium on Oxygen Consumption and the ATP/ADP Ratio Within Photoreceptors. Invest. Ophthalmol. Vis. Sci. 2007;48(13):589.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Calcium is a critical signal in mediating the response of photoreceptors to light. cGMP synthesis and rhodopsin phosphorylation are both influenced by calcium. We hypothesize that in contrast to many other tissues, where calcium stimulates oxidative metabolism by increasing the rate of the TCA cycle and the work of ion transport¹, the regulation of photoreceptor energetics by calcium may be different. To address this question we developed methods to quantify oxygen consumption and energetic nucleotide ratios in photoreceptors of functional mouse retinas.
C57Bl/6 mice were dark adapted overnight and then euthanized. We enucleated the eyes and dissected the retinas into an oxygenated physiological buffer with glucose that either contained or lacked calcium. The retinas were frozen with liquid nitrogen and then homogenized in ice cold 0.5 M perchloric acid. Nucleotide levels within the extracts were measured by ion exchange HPLC. Peaks were identified using nucleotide standards. Oxygen consumption was monitored using a perfusion system². To monitor retinal oxygen consumption in the absence of photoreceptors we used adult AIPL1-/- retinas. All measurements were done in darkness using only infrared illumination.
By comparing normal retinas to retinas without photoreceptors we confirmed that the majority of oxygen consumed by mouse retinas occurs in photoreceptors. Oxygen consumption analysis showed that there is a significant, but transient, burst of energy use and production upon removal of calcium. A substantial drop in the GTP to GDP ratio also occurred when calcium was removed from the extracellular medium. The latter observation is consistent with known biochemical activities. In low calcium in darkness the guanylyl cyclase is active and the phosphodiesterase is inactive so guanine nucleotides accumulate in the form of cGMP.
Calcium inhibits oxygen consumption and energy usage by mouse retinas in contrast to other tissues where it stimulates oxygen consumption. The techniques we developed are effective at monitoring energy production and control within the retina. Using these methods and using various mutant mouse strains we will be able to evaluate the contributions of specific phototransduction reactions to energy consumption in photoreceptors.¹Sweet, I.R., Gilbert, M. (2006). Contribution of calcium influx in mediating glucose-stimulated oxygen consumption in pancreatic islets. Diabetes 55: 3509-19.²Sweet, I.R., et al. (2004). Regulation of ATP/ADP in pancreatic islets. Diabetes 53: 401-409.
This PDF is available to Subscribers Only