title: Relationship of stokes radius to the rate of diffusion across Bruch's membrane.
abstract: OBJECTIVE
  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 tracers with R(S) values ranging from <1.0 to 6.15 nm. Samples were collected from both chambers at various time points up to 36 hours 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 hours 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 tracers: 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 tracers. We have successfully demonstrated that quantitative gel exclusion chromatography can be used to follow diffusion of a mixture of tracers 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).
authors.affiliation: Department of Ophthalmology and Vision Science, University of Arizona, Tucson, Arizona 85724, USA.
authors.forename: Astrid
authors.initials: A
authors.lastname: Zayas-Santiago
authors.forename: Alan D
authors.initials: AD
authors.lastname: Marmorstein
authors.forename: Lihua Y
authors.initials: LY
authors.lastname: Marmorstein
mesh_terms: D000818:Animals; D001692:Biological Transport; D016570:Bruch Membrane / Q000378:metabolism* / Q000648:ultrastructure; D002463:Cell Membrane Permeability / Q000502:physiology*; D002850:Chromatography, Gel; D004195:Disease Models, Animal; D046911:Macromolecular Substances / Q000493:pharmacokinetics*; D008268:Macular Degeneration / Q000378:metabolism / Q000473:pathology; D008855:Microscopy, Electron, Scanning; D012709:Serum Albumin / Q000493:pharmacokinetics*; D013552:Swine
chemical_list: D046911:Macromolecular Substances; D012709:Serum Albumin