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B.P. Danysh, M.K. Duncan; Quantitative Measurement of Lens Capsule Permeability . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4098.
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© ARVO (1962-2015); The Authors (2016-present)
The lens capsule serves as a selective barrier between the lens and ocular environment. The nature of this selectivity was first investigated by Friedenwald in 1929, although quantitative measurements were impossible on intact lenses due to limitations on the available methods. In general the physical properties of molecules able to diffuse through the capsule and their diffusion rates are not well characterized.
Fluorescence Recovery After Photobleaching (FRAP) is a method that allows the quantification of diffusion rates for molecules in a matrix. Fresh mouse lenses were isolated and their capsules loaded with FITC–dextrans of various sizes as well as non–linear fluorescent labeled molecules. Diffusivity of the molecules tested was derived from the FRAP data obtained. The thickness of capsules from FVB/NTac mice, 129X1/SvJ mice, and 129X1/SvJ mice containing a functional knockout for the col4a3 gene was measured using confocal Z–axis imaging of lenses loaded with fluorescent molecules.
Uncharged FITC–dextran molecules with molecular weights ranging between 3kDa to 150kDa and Stokes radii between 1nm to 8.5nm were found to enter the capsule. The diffusion coefficient of 150kDa FITC–dextran was 2X slower than the 10kDa version and 4.5X slower than the 4kDa version. Immunoglobulin has a significantly smaller Stokes radius than 150kDa FITC–dextran but diffuses at a slower rate. A 40% difference in capsule thickness was found between two mouse species, 129X1/SvJ and FVB/NTac. 129X1/SvJ col4a3 KO mice (lacking the Collagen IV α3•α4•α5 network) had capsules 15% thinner than WT of the same strain.
The differences in capsule thickness between 129X1/SvJ and FVB/NTac mouse strains may suggest differences in capsule synthesis and degradation. The 129X1/SvJ col4a3 KO mice showed thinning of the lens capsule consistent with phenotypes reported in human Alport’s Syndrome patients possibly due to the collapsing of the capsule matrix lacking the α3•α4•α5 network. FVB/NTac capsules were readily permeable to neutral FITC–dextran molecules of Stokes radii similar to many of the components of the aqueous and vitreous humor. Both charge and Stokes radius significantly influence diffusion rates through the lens capsule.
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