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GJ Baldo, J Gao, X Sun, RT Mathias; Intracellular Ca2+-Concentration Gradient Within the Lens . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3539.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Cataracts may be directly associated with perturbations in levels of Ca2+ within the lens. In the present study, we investigated [Ca2+]i at different depths within normal frog and mouse lenses. Methods: All experiments were conducted on freshly dissected frog and mouse lenses. Because the lens absorbs light at the wavelengths of interest, calibration changed with depth into the lens. To obtain depth-dependent calibration curves, we inserted a long sharp glass pipette, containing an intracellular-like solution with known free [Ca2+] plus 2 - 5 mM fura-2, into the center of lenses from either frogs or mice. Images at wavelengths 360 nm and 380 nm were acquired. We divided the distance from the surface of the lens to its center into 7 equal length sections. The ratio of fluorescence at 360 nm to that at 380 nm in different [Ca2+] in each section was determined, then 7 calibration curves, ratios vs [Ca2+], were established for each species. We injected 2 mM fura-2 into the fiber cells at different depths into lenses from each species, acquired the images and determined the ratios of fluorescence at 360 nm to that at 380 nm. These ratios were converted into [Ca2+]i with the Ca2+-calibration curve from the appropriate depth. Results: Intracellular Ca2+-concentration increased continuously as a function of distance from the lens surface. In 35 frog lenses, the average diameter was 4.23±0.24 mm. Fiber cells at a distance of 154 µm from the surface had a [Ca2+]i of 109 nM, at 0.86 mm into the lens [Ca2+]i was 285 nM, and at 1.55 mm from the surface (564 µm from the center) [Ca2+]i was 718 nM. In 30 mouse lenses, the average diameter was 2.05±0.05 mm. Fiber cells at a distance of 162 µm from the surface had a [Ca2+]i of 137 nM, at 0.62 mm into the lens [Ca2+]i was 275 nM, and at 0.93 mm (92 µm from the center) [Ca2+]i was 436 nM. Conclusion: Our results suggest there is a [Ca2+]i-gradient in the lens with a lower [Ca2+]i near the surface and a higher [Ca2+]i at the center. Our earlier report (IOVS 42(4), s540, 2001) suggested the lens has significant Na/Ca exchange, which works in concert with the Na/K ATPase to regulate [Ca2+]i. Compromise of either transporter will cause [Ca2+]i to increase, and possibly induce a central cataract
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