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R. McNulty, R.J. Truscott, S. Bassnett; Lens pO2 Gradients in vitro: Controlling Mechanisms . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3140.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: O2 is implicated in the formation of age-related nuclear cataract. Previously we showed that pO2 values in the core of the lens are very low (ARVO abstract #2374, 2002). Here, we examine factors that influence the shape and magnitude of cortical O2 gradients in bovine and human lenses in vitro. Methods: Lens pO2 was determined in vitro by inserting a fine, fiber optic-based O2 sensor (OxyLab, Oxford Optronix) into the lens. Tissue O2 consumption was measured using a respirometer (model 5300 YSI, OH). The distribution of mitochondria was visualized by 2-photon microscopy following incubation with rhodamine 123. Results: When incubated with solutions containing physiologically relevant concentrations of O2 (1-5% O2), a sharp standing gradient of pO2 was established in the cortex of human and bovine lenses. As a result, pO2 in the lens interior was extremely low (1-2 mmHg). Furthermore, core pO2 was relatively insensitive to increases in external pO2. The most reliable method for increasing lens core pO2 was to lower the temperature. A 19oC reduction in temperature resulted in a decrease in lens oxygen consumption from 9.8 to 1 µl/g/hr and a concomitant, reversible increase in core pO2. We examined the contribution of oxidative phosphorylation to the creation of bovine lens pO2 gradients by treating lenses with the mitochondrial poisons azide and 3-NP, or removing the mitochondria-rich lens cortex. Neither treatment completely abolished the pO2 gradient. By 2 photon microscopy, mitochondria were found to be present to a depth of 500 µm at the bovine lens poles and 725 µm at the lens equator. Significantly, intra-lenticular pO2 gradients extended well beyond these depths. Conclusions: O2 consumption by the lens results in an internal pO2 much lower than that of its environment. Both oxidative phosphorylation in the mitochondria-rich surface layers and non-mitochondrial processes contribute to lens O2 consumption and pO2 gradients.
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