Charge modification of the endothelial surface layer modulates the permeability barrier of isolated rat mesenteric small arteries

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Abstract
We hypothesized that modulation of the effective charge density of the endothelial surface layer (ESL) results in altered arterial barrier properties to transport of anionic solutes. Rat mesenteric small arteries (diameter ∼190 μm) were isolated, cannulated, perfused, and superfused with MOPS-buffered physiological salt solutions. MOPS-solutions were of normal ionic strength (162 mM, MOPS), low ionic strength (81 mM, LO-MOPS), or high ionic strength (323 mM, HI-MOPS), to modulate ESL charge density (normal, high, or low ESL charge, respectively). Osmolarity of MOPS, LO-MOPS, and HI-MOPS was kept constant at 297 mosmol/l, using additional glucose when necessary. Perfusate solutions were supplemented with 1% BSA. Arteries were cannulated with a double-barreled theta-pipet on the inlet side and a regular pipet on the outlet side. After infusion of FITC-labeled dextran of 50 kDa (FITC-Δ50) and the endothelial membrane dye 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate, the dynamics of arterial dye filling were determined with confocal microscopy. ESL thickness, as determined from the initial exclusion zone for FITC-Δ50 on the luminal endothelial surface, was 6.3 ± 1.4 μm for LO-MOPS, 2.7 ± 1.0 μm for MOPS, and 1.1 ± 1.3 μm for HI-MOPS. At low ionic strength, FITC-Δ50 permeated into the ESL with a total ESL permeation time (τESL) of 26 min, and at normal ionic strength with a τESL of 20 min. No apparent exclusion of FITC-Δ50 from the ESL could be observed at high ionic strength. In conclusion, we demonstrate that the modulation of solvent ionic strength influences the thickness and barrier properties of the ESL.