TRANSPORT VIA MATRIX FILLED CAPILLARY CLEFTS: EFFECTS OF ELECTROKINETICS

University Of Washington, Seattle WA

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Abstract

Experimental measurements of transcapillary permeability of charged and neutral molecules of equal size suggest molecular charge is an important determinant of microvascular permeability. We investigate contributions of solute and barrier charge to capillary permselectivity in a continuum model of electrokinetic and convective transcapillary exchange. The exchange barrier is modelled with parallel plates representing endothelial cell surfaces and a bridging hexagonal array of posts representing glycocalyx fibers as described by Curry (1984) and Weinbaum et al. (1992). Cleft and post surfaces are held at constant zeta potential. For a single post bridging the region between two parallel plates, the linear Poisson-Boltzmann and modified Stokes equations are solved using boundary element computational methods for the electrostatic potential and convective velocity profile, respectively. For plate separation (130 A), post radius (6 A), Debye length (8 A) and zeta potential values (-60 mV) typical of plasma ultrafiltrate in a glycocalyx filled interendothelial cleft, the electrostatic potential decays with distance from the post surface, vanishing at approximately 5 Debye lengths. Thus, compared to neutral molecules, there is enhanced anionic and diminished cationic convective transport in this region near the post for negative zeta potentials characteristic of plasma membranes and glycocalyx. The effect is more pronounced near plate surfaces. This computational result demonstrates contributions of electrostatic forces to charged particle transport as observed in certain experimental studies.