The contribution of solute-solvent exchange at the membrane surface to the reduction by albumin of the hydraulic permeability coefficient of an artificial semipermeable membrane.

Abstract

Infusion of synthetic colloids for tissue edema in inflammatory conditions reduces the hydraulic permeability coefficient (L(p)) of capillary membranes. However, the molecular mechanisms governing the modulation of L(p) of capillary membranes by these colloidal macromolecules are not known. In this study, I examined the effect of albumin on the L(p) of an artificial semipermeable membrane to determine whether solute-solvent exchange at the membrane surface may contribute to reduction of the L(p) of capillary membranes by colloidal macromolecules. The artificial membrane was used because of its well known molecular weight cutoff size and the absence of any specific interaction of albumin with such membranes. L(p) values of ultrafiltration membranes (molecular weight cutoff, 30,000) were measured by using an osmotic flow cell at a hydrostatic pressure difference (DeltaP) of 30 cm H(2)O in the absence of albumin or in the presence of albumin (2.4-8 wt%) at a DeltaP of 0 or 30 cm H(2)O. At all concentrations, albumin decreased L(p) values at both DeltaP values of 0 and 30 cm H(2)O compared with those in the absence of albumin (P < 0.05). These reductions were almost in a concentration-dependent manner and by almost half at 8 wt% albumin. This finding may be appropriately explained by slowed solute-solvent exchange at the membrane surface as the albumin concentration is increased. It is concluded that the reduction in the L(p) of capillary membranes by colloidal macromolecules is not caused solely by plugging of the capillary pores, but also by solute-solvent exchange at the capillary membrane surface. Albumin concentrations more than 2.4 wt% decreased the water permeabilities of ultrafiltration membranes compared with those measured in the absence of albumin. The finding may be explained by slowed solute-solvent exchange at the membrane surface, suggesting that the reduction in water permeability of capillary membranes by colloidal macromolecules may not be caused solely by plugging of the capillary pores.