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 ( Delta P) 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 Delta P. 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.s(-1).cmH(2)O(-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 Delta P 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 Delta P of 40-45 cmH(2)O 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.