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Jack V Greiner, Thomas Glonek; Comparing the Hydrotropic Function of ATP in Ocular Tissues with High and Low Metabolic Activity. Invest. Ophthalmol. Vis. Sci. 2020;61(7):784.
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© ARVO (1962-2015); The Authors (2016-present)
Unexplainably high millimolar (3.0mM) concentrations of ATP exist in the crystalline lens when all of the known functions of ATP, combined, require only micromolar (μM) concentrations. At high mM concentrations ATP functions as a hydrotrope preventing protein aggregation. This high mM concentration of ATP is inconsistent, since the lens is known to be metabolically quiescent, when compared to retinal tissue. The purpose of this study was (1) to compare the 31P energy modulus by magnetic resonance spectroscopy (MRS) to establish the metabolic status of lenticular and retinal tissues, and (2) to determine the ATP concentration in these tissues.
Fresh rat lenses (n=24) were pooled in 4 groups each with 6 lenses; retinas (n=90) were pooled in 3 groups each with 30 retinas. PCA extractions were performed and quantitative 31P MRS used to measure the mole fractions of ATP and spectral profiles of 8 high- and 21 low-energy phosphatic metabolites. The 31P energy modulus was an index calculated by dividing the total high-energy metabolites by the low-energy metabolites.
The 31P energy modulus of lens was 1.09±0.03 and of retina 1.27±0.05. Although these numbers may be different, this conclusion must be made with caution considering the influence of tissue dissection techniques. ATP concentration in the lens was 41.0±0.07% and retina 21.1±1.44% (p <0.001).
Although the metabolic activity of the retina might be expected to be an order-of-magnitude greater than the lens, such a difference in the 31P energy modulus, a measure of high-energy phosphate concentration, was not observed. The mM concentration of ATP in both lens (3.0mM) and retina (2.4mM) far exceeds the μM amount of ATP required to carry out metabolic functions. More surprisingly the lens had nearly twice the concentration of ATP compared to the retina. Since a high mM concentration of ATP is required to function as a hydrotrope in preventing protein aggregation and disease, it is hypothesized that membrane proteins in neural retina may require a lesser degree of ATP for maintenance in preventing protein aggregation in contrast to lens, a tissue with the highest concentration of proteins in the body. Although both lens and retina have high mM concentrations of ATP the need for high-energy phosphate functioning as a hydrotrope may be lower in the retina though its metabolic status appears comparable to the lens.
This is a 2020 ARVO Annual Meeting abstract.
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