Macromolecular transport across endothelial monolayers.

We studied the macromolecular size-selective transport characteristics of polycarbonate (PC) filters with defined pore radius (rp; 15,000 to 400 A) as well as 2,000 A rp PC filter-bovine pulmonary artery endothelial cell (EC) monolayer sandwich under zero hydrostatic pressure conditions using fluorescein isothiocyanate-hydroxyethyl starch (FITC-HES, 16 A less than ae less than 100 A), and 2-methoxy-2,4-diphenyl-3(2H) furanone-bovine serum albumin (MDPF-BSA, ae = 35.5 A). We surprised to find substantial convective solute transport (solute drag) across the filter-endothelial sandwich. This effect was increased by large rp (15,000 A) filters and prevented by 400 A rp filters. Positive hydrostatic pressure across 2,000 A rp filters increased convective solute transport and negative pressure prevented this effect. High, medium and low permeability monolayers on 2,000 A filters progressively attenuated the solute drag effect seen across these filters without cells. The decline in monolayer permeability was associated with an increased filter area covered by cells; approximately 50 and 95% as well as greater than 99%, respectively. Although significant restricted diffusion was seen across low permeability monolayers, this pattern was distinct from that measured in single frog capillaries. Restricted diffusion by low permeability monolayers under conditions that produce solute drag document the significant barrier effects of high confluence endothelial monolayers, in vitro. These data show that solute transport across endothelial monolayers is due to diffusion+convective solute drag. The degree of the solute drag effect across the filter-endothelial sandwich is a direct function of monolayer confluence.