Temperature dependence of macromolecular sieving across plasma fractionating membranes

The temperature dependence of macromolecular sieving coefficients (S) across a plasma fractionating membrane due to changes in the intrinsic process of membrane filtration was determined using dextrans as test macromolecules. Sieving coefficients were determined in an in vitro test circuit as a function of time, temperature, flow conditions, and plasma protein exposure. Sieving coefficients for albumin, gamma G immunoglobulin (IgG), and dextrans using normal human plasma as the test solution were comparable for dextrans and proteins of equivalent molecular size, independent of time after 15 min, lower at 8 degrees than at 37 degrees C, and higher at lower filtration flow rates. At 8 degrees C and high filtration flow rates, S for albumin and IgG also increased with increasing perfusate flow rate. Dextran S using a protein-free test solution before exposure to plasma were higher than those determined from plasma, and were independent of temperature. Dextran S from a protein-free test solution after exposure to plasma were similar to those determined from plasma at 37 degrees C, but higher than those determined from plasma at 8 degrees C. We conclude that sieving coefficients across plasma fractionating membranes can be altered by temperature due to changes in the process of membrane filtration. The present observations suggest that at low temperature a polarized layer or gel becomes a discriminating solute transport barrier.