DETERMINATION OF SYSTEMIC VASCULAR GLYCOCALYX VOLUME IN MICE

Abstract

Intravital microscopic studies in cremaster muscle capillaries indicate the presence of a ~0.5 μm thick endothelial glycocalyx which excludes flowing blood and anionic dextrans of 500 kDa (D500) and 70 kDa (D70), but is fully accessible to neutral dextrans of 40 kDa (D40) (Vink & Duling, 1996, 2000). In the present study we determined glycocalyx exclusion volumes (Vg, in ml) of circulating plasma, D500, and D70 in the systemic circulation in mice by comparing their systemic vascular distribution volume (Vd, in ml) to that of D40. Fluorescently labelled red blood cells (RBCs) and dextrans were i.v. infused in anesthetized C57Bl/6 mice and blood samples subsequently collected by tail bleeding. Plasma Vd was calculated from the steady-state dilution of RBCs and hematocrit, and was 0.72 ± 0.03 (n=4). Dextran Vd was derived from the plasma concentration 30 s after injection, and was 0.82 ± 0.09 for D500 (n=6), 0.92 ± 0.06 for D70 (n=6), and 0.96 ± 0.04 for D40 (n=16). Vg for plasma, D500, and D70 was 0.39 ± 0.04, 0.18 ± 0.04, and 0.05 ± 0.02, respectively. Our data indicate the presence of a glycocalyx of ~0.4 ml in the systemic circulation in mice that partially excludes plasma macromolecules in a size dependent manner. Support: Netherlands Organization of Scientific Research (NWO, #902-16-192, JWvT) & Royal Netherlands Academy of Sciences (to HV).