FLOWS OF LIQUID AND ELECTRICAL-CURRENT THROUGH MONOLAYERS OF CULTURED BOVINE ARTERIAL ENDOTHELIUM

1. Monolayers of arterial endothelium on porous membranes were exposed to a constant pressure between 15 and 35 cmH2O. The rates of liquid flow per unit area (J(v)/A) through the monolayers were monitored, together with the electrical resistance (R(m)) of the endothelium. 2. At constant pressure, J(v)/A decreased with an approximately exponential time course, towards a stable baseline value. This behaviour resembles the sealing previously described for cultured vascular endothelium. At 30-35 cmH2O and 37-degrees-C, the mean (+/- S.E.M.) half-time (t1/2) of the decrease in J(v)/A (the sealing t1/2) was 548 +/- 141 s (n = 5). The difference between the initial and baseline values of J(v)/A was expressed as a fraction of the initial value. The mean (+/- S.E.M.) of this sealing fraction was 0.64 +/- 0.03 (n = 5). Mean (+/- S.E.M.) hydraulic permeability (L(p)) was 23.9 +/- 6.4 x 10(-7) cm s-1 cmH2O-1 (n = 9), when measured after sealing. Endothelium appeared damaged after sealing at 30-35 cmH2O and 37-degrees-C. 3. Sealing was also observed using glutaraldehyde-fixed endothelium at 30-33 cmH2O and 26-28-degrees-C. There was no significant difference between the mean sealing t1/2 of these fixed monolayers, and that of unfixed endothelium at 30-35 cmH2O and 37-degrees-C. However, mean sealing fraction was significantly larger for the fixed monolayers than for unfixed endothelium at 30-35 cmH2O and 37-degrees-C. There was no significant difference between the post-sealing L(p)s of these fixed and unfixed monolayers, although the fixed monolayers appeared undamaged after sealing. 4. For unfixed endothelium, R(m) was lower after sealing at 30-35 cmH2O and 37-degrees-C than before pressure application. There was no significant difference between endothelial R(m) before and after sealing, for glutaraldehyde-fixed monolayers. 5. Sealing was also observed at 0-degrees-C, using unfixed endothelium at 30 cmH2O. Mean sealing t1/2 was not significantly different from that of unfixed endothelium at 30 cmH2O and 37-degrees-C. However, mean sealing fraction was significantly smaller at 0-degrees-C than at 37-degrees-C. Unfixed endothelium appeared undamaged after sealing at 30 cmH2O and 0-degrees-C. Despite this, the post-sealing L(p) was not significantly different from that of unfixed endothelium sealed at 30 cmH2O and 37-degrees-C, after allowance was made for the effect of temperature on L(p). R(m) was not measured in these experiments. 6. It is proposed that sealing is due to pressure-induced deformation of monolayers. The similar L(p)s of damaged and undamaged endothelium can be accounted for if a substantial proportion of monolayer hydraulic resistance is due to extracellular material. The paradoxical changes in L(p) and R(m) during sealing can be accounted for in a similar way.