Hydraulic conductance of pulmonary microvascular and macrovascular endothelial cell monolayers

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 (deltaP) was controlled by the reservoir height, and the filtration rate corrected for surface area (J(v)/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 J(v)/A on deltaP. 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 x 10(-7) cm x s(-1) x cmH2O(-1); P < or = 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 deltaP in RPMVEC monolayers > or = 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 deltaP of 40-45 cmH2O for 2 h, J(v)/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.