Solute transport to the endothelial intercellular cleft: the effect of wall shear stress

The interendothelial cleft is the major transport pathway across the endothelium for hydrophilic solutes including albumin and low density lipoprotein. Previous models of arterial wall transport have assumed that the entire endothelial cell surface is available for transport from the fluid (blood) phase. One of the consequences of a cleft-mediated solute uptake mechanism is the limited area available for mass transport. This effect, together with the influence of a predominantly longitudinal cleft orientation in relation to flow, dramatically alters the fluid-phase mass transport characteristics relative to what has been assumed previously in analyzing vascular solute uptake problems. We have used a finite element computational model to simulate fluid phase transport to a longitudinal endothelial cleft under realistic wall shear rate conditions. Our numerical results show reduced dependence of the mass transfer rate on the wall shear rate compared to the classical Leveque solution for mass transport in a cross-flow configuration and confirm the significance of the wall and not the fluid as the limiting resistance to transport of macromolecules.