Determination of Microvessel Permeability and Tissue Diffusion Coefficient of Solutes by Laser Scanning Confocal Microscopy

Abstract

Interstitium contains a matrix of fibrous molecules that creates considerable resistance to water and solutes in series with the microvessel wall. On the basis of our preliminary studies (, 1994, Microcirculation1(4), pp. 251–265; , 1995Am. J. Physiol.269(38), pp. H2124–H2140), by using laser-scanning confocal microscopy and a theoretical model for interstitial transport, we determined both microvessel solute permeability (P) and solute tissue diffusion coefficient (Dt) of α-lactalbumin (Stokes radius 2.01nm) from the rate of tissue solute accumulation and the radial concentration gradient around individually perfused microvessel in frog mesentery. Pα‐lactalbumin is 1.7±0.7(SD)×10−6cm∕s(n=6). Dt∕Dfree for α-lactalbumin is 27%±5%(SD)(n=6). This value of Dt∕Dfree is comparable to that for small solute sodium fluorescein (Stokes radius 0.45nm), while Pα‐lactalbumin is only 3.4% of Psodiumfluorescein. Our results suggest that frog mesenteric tissue is much less selective to solutes than the microvessel wall.