Effect of albumin on the width of water channels in venous endothelium

Abstract

The effect of bovine and dog albumin and plasma was measured on the hydraulic conductivity (Lp) and electrical resistance (R) across the endothelium of the dog vena cava. An estimate of changes in size of transendothelial water channels was then obtained by combining Lp and R values. Dogs were anesthetized with pentobarbital sodium to surgically remove their thoracic inferior vena cava. Lp was measured by a gravimetric method at constant vessel volume. R was obtained from the transvascular voltage changes caused by current pulses. Lp measured at the beginning of the experiments was 0.97 +/- 0.17 X 10(-7) cm.s-1.cmH2O-1 in plasma and 2.75 +/- 0.48 X 10(-7) cm.s-1.cmH2O-1 in Ringer solution. Bovine albumin produced an 18% reduction in Lp relative to its value in Ringer solution. Dog albumin and plasma lowered Lp 50 and 54%, respectively. The differences were statistically significant with P less than 0.05. R increased from 15.17 +/- 7.0 to 26.5 +/- 16.0 omega.cm2 in dog albumin and 27.4 +/- 9.6 omega.cm2 in dog plasma. Calculations using a model for the transendothelial channel and equations for Lp and R showed a decrease in channel width of 172 A due to the protein. This could be accounted for by the thickness of a monolayer of albumin absorbed to the channel walls. Results suggest that the permeability response to plasma proteins is a general property of vascular endothelium.