Hydraulic conductance of pulmonary microvascular and macrovascular endothelial cell monolayers

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Abstract
Endothelial cells isolated from pulmonary arteries (RPAEC) and microcirculation (RPMVEC) of rat lungs were grown to confluence on porous filters and mounted on an Ussing-type chamber. Transmembrane pressure (ΔP) was controlled by the reservoir height, and the filtration rate corrected for surface area ( Jv/ A) was measured by timing fluid movement in a calibrated micropipette. These parameters were used to calculate hydraulic conductance (Lp) by using linear regression of Jv/ A on ΔP. Mean Lp values for newly confluent RPAEC monolayers were 22 times higher than those for RPMVEC monolayers (28.6 ± 5.6 vs. 1.30 ± 0.50 × 10−7 cm·s−1·cmH2O−1; P ≤ 0.01). After confluence was reached, electrical resistance and Lp remained stable in RPAEC but continued to change in RPMVEC with days in culture. Both phenotypes exhibited an initial time-dependent sealing response, but Lp also had an inverse relationship to ΔP in RPMVEC monolayers ≥4 days postconfluence that was attributed to cell overgrowth rather than junctional length. In a comparison of the cadherin contents, E-cadherin was predominant in RPMVEC, but VE-cadherin was predominant in RPAEC. At a constant ΔP of 40–45 cmH2O for 2 h, Jv/ A increased 225% in RPAEC monolayers but did not change significantly in RPMVEC monolayers. Significant decreases in Lp were obtained after treatment with 5% albumin, GdCl3, or isoproterenol plus rolipram in both phenotypes. Thus lung microvascular endothelial cells exhibited a significantly lower Lp than conduit vessel endothelium, which would limit alveolar flooding relative to perivascular edema cuff formation during increased pulmonary vascular pressures.

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