ALBUMIN AND RICINUS-COMMUNIS AGGLUTININ DECREASE ENDOTHELIAL PERMEABILITY VIA INTERACTIONS WITH MATRIX

We studied the effects of albumin and the lectin Ricinus communis agglutinin (RCA) on hydraulic conductivity (L(p)) of bovine pulmonary microvascular endothelial cell monolayers (BPMVEC) because of the evidence that albumin and RCA can interfere with transendothelial albumin permeability (Siflinger-Bimboim, A., J. Schnitzer, H. Lum, F. Blumenstock, C. Shen, P. Del Vecchio, and A. Malik. J. Cell. Physiol. 149: 575-584, 1991). BPMVEC were seeded on microporous polycarbonate filters, and the liquid flux was measured by collecting effluent into a tubing of known inner diameter at transendothelial hydrostatic pressures (P) ranging from 5 to 20 cmH2O. L(p) was calculated as the slope of the relationship of liquid flux per unit surface area (J(v)) vs. P. Addition of RCA (50 mug/ml) or albumin (5 mg/ml) to the endothelial cell medium containing albumin-free Hanks' balanced saline solution (HBSS) decreased total L(p) (expressed x 10(-6) cm.s-1.cmH2O-1) from 17.2 +/- 3.6 during HBSS to 4.7 +/- 0.9 during albumin and 5.7 +/- 1.6 during RCA (P < 0.01 for both). The RCA effect, but not that of albumin, was prevented by the addition of D-galactose (0.1 M) (the cognate hapten monosaccharide of RCA). We determined the contribution of the extracellular matrix (ECM) in decreasing the L(p) by obtaining ECM after treatment of the monolayers with 0.025 M NH4OH to detach endothelial cells from the ECM. Basal ECM L(p) (expressed x 10(-6) cm . s-1 . cmH2O-1) was 57.0 +/- 15.3, and it decreased to 19.7 +/- 4.3 and 17.5 +/- 2.9 during RCA and albumin, respectively (P < 0.01 for both). In contrast, RCA and albumin did not alter the filter L(p) values. Another lectin, Ulex europaeus agglutinin, and the protein immunoglobulin G had no effect on L(p) values. Western blot analysis showed that both albumin and RCA bind to ECM, but to different ECM constituents. We postulate that albumin and RCA can decrease the transendothelial liquid permeability by interacting with distinct ECM proteins.