PROTEIN-MEMBRANE INTERACTIONS DURING HEMODIALYSIS - EFFECTS ON SOLUTETRANSPORT

Although several previous studies have shown that plasma protein adsor ption can reduce solute clearance during hemodialysis, there is curren tly no quantitative understanding of the factors that govern the exten t of these protein-membrane interactions. In this study, quantitative data were obtained for the clearance of urea, vitamin B-12, and polydi sperse dextrans using polyacrylonitrile (AN69) and cellulose triacetat e dialyzers before and after exposure to human plasma in a simulated d ialysis session. Contact with plasma had little effect on clearance of urea and vitamin B-12, but caused more than an order of magnitude red uction in clearance for solutes with molecular weights >10,000. These data were analyzed using a two layer model in which contact with plasm a was assumed to cause a thin protein layer to form on the surface of the membrane. The protein layer had an effective pore size of approxim ate to 12 Angstrom, and was approximate to 1 mu m thick, as determined by a hydrodynamic analysis of the clearance data, and from independen t estimates based on changes in fiber bundle volume and ultrafiltratio n coefficient. The thickness of the protein layer increased with incre asing dialysis time, ranging from 0.25 mu m after 40 min to 0.86 mu m after 180 min. These results provide important insights into the effec ts of contact with plasma on solute clearance during hemodialysis.