Relationship of stokes radius to the rate of diffusion across Bruch's Membrane

Abstract

Purpose. To determine the effect of Stokes radius (R S) on the diffusion of molecules through Bruch's membrane (BM), and to establish a system suitable for the analysis of diffusion through small (<2 mm 2) samples of BM. Methods. Porcine BM/choroid (BM/Ch) was mounted in a modified Ussing chamber. A concentration gradient was simultaneously established for four traceR S with R S values ranging from <1.0 to 6.15 nm. Samples were collected from both chambeR S at various time points up to 36 houR S and the amount of each tracer was determined using quantitative gel exclusion chromatography. The integrity of samples was determined using scanning electron microscopy. Results. BM/Ch mounted in the chamber exhibited no obvious damage even after 36 houR S in the chamber. Flux was significantly (P < 0.05) greater in the BM to Ch direction than that in the Ch to BM direction for only two of the traceR S: cytosine and RNase A. Flux also was dependent on R S; cytosine, the smallest tracer (R S < 1 nm), exhibited the greatest flux and ferritin (R S = 6.15 nm) the least. Permeability coefficients for each tracer were determined and exhibited a power relationship with R S. Conclusions. Flux was dependent on the direction of the concentration gradient and the R S of the individual traceR S. We have successfully demonstrated that quantitative gel exclusion chromatography can be used to follow diffusion of a mixture of traceR S across BM/Ch, and that we can measure flux across BM/Ch preparations with an exposed surface area as small as 1.8 mm 2. © 2011 The Association for Research in Vision and Ophthalmology, Inc.