Fiber matrix descriptors from permeability data without requiring membrane thickness: theory, results, and optimization.
OBJECTIVE
Permeability of basement membrane and all other barriers contains a term for membrane thickness (delta x). This naturally leads to development of methods for measuring delta x that are imprecise, inaccurate, expensive, subject to preparation artifact, and inattentive to variability. Although height and shape of permeability (P) vs. probe radius (aE) curves are sensitive to delta x, In(P) or In (P/free diffusivity or D0) curves have shapes independent of delta x. It should, thus, be possible using such characteristics to determine fiber radius (rf) and void volume ratio (epsilon) without delta x. We developed such a method to derive membrane structure by the standard model of Ogston and present its experimental evaluation.


METHODS
Basement membranes were self-assembled using 1:1 Matrigel: 0.01 M Tris/150 mM NaCl/1.0 mM CaCl2 buffer on 0.4-mu polycarbonate supports with transport measured in diffusion chambers using FITC-labeled hydroxyethyl starch probes from 25 to 102 A in radius. Sampling was at 0.5 hr and then for each hour up to 5. Other membranes were measured 7 days after formation.


RESULTS
The best fit of the new technique occurred at 3 hr with R2 = 0.949 +/- 0.003 SEM, rf = 36.8 = 2.4 A, and epsilon = 0.87 +/- 0.02. Membranes studied for 7 days showed more variability but essentially the same characteristics.


CONCLUSIONS
Membrane thickness is not necessary to reduce permeability of basement membrane to structure, and optimum sampling time is 3 hr.
Katz
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Benjamin W. Zweifach Microcirculation Laboratories, Tucson Veterans Affairs Medical Center, Arizona, USA.
LaMarche
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D000818:Animals; D001485:Basement Membrane / Q000648:ultrastructure; D002463:Cell Membrane Permeability; D051379:Mice; D008954:Models, Biological; D012513:Sarcoma, Experimental / Q000648:ultrastructure