Endothelial surface charge of intestinal mucosal capillaries and its modulation by dextran

Capillary endothelial surface charge was investigated by perfusing the intestinal circulation of anesthetized rats in situ with 0.1 or 10 mg/ml native ferritin (NF, pI = 3.8-4.2) or with 0.1 mg/ml cationized ferritin (CF, pI greater than 10.0) for 5 min, with or without 5% Dextran 40. Ferritin binding was quantified by electron microscopy. All electron micrographs of capillaries perfused with NF showed some NF binding. Mean NF particle densities (particles/microns) were significantly greater at vesicle necks (PDv) than elsewhere on the endothelial surface (PD). Capillaries perfused with CF showed binding in only 60% of the transverse sections examined. The binding was very marked in a large proportion of these vessels. Mean CF particle densities were significantly greater at fenestrae (PDf) than elsewhere. These results demonstrate that mucosal capillaries have a variable negative electrostatic charge on the endothelial surface and support the hypothesis that some vesicle diaphragms act as preferential attractors for anionic macromolecules. Such structures could promote transendothelial vesicular transport of albumin. Dextran significantly decreased PD for NF from 25.4 +/- 2.4 (SEM) to 13.1 +/- 0.9 and PD, PDv, and PDf for CF from 45.9 +/- 4.6 to 31.0 +/- 2.7, from 62.1 +/- 6.2 to 43.6 +/- 5.4, and from 152.9 +/- 15.5 to 114.5 +/- 8.6, respectively. The above responses result from dextran's weak interaction with the endothelial surface. Dextran reduces access of ferritin molecules to the cell surface by steric hindrance and/or electrostatic shielding of the glycocalyx.