Glycophorin incorporation increases the bilayer permeability of large unilamellar vesicles in a lipid-dependent manner

Abstract

(1) The effect of glycophorin incorporation on the permeability properties of lipid bilayers is investigated by employing a new method, in which the trap of a small permeant and a high molecular weight, non-permeable molecule are simultaneously monitored. (2) Glycophorin induces a high permeability to potassium and glucose in large dioleoylphosphatidylcholine vesicles. (3) The glycophorin-induced enhanced permeability is found to be lipid dependent. By monitoring the % ratio of the glucose (permeant)/dextran (impermeant) trap in large unilamellar glycophorin-containing vesicles, it was determined immediately after removal of non-enclosed marker, that glycophorin-containing vesicles composed of dioleoylphosphatidylcholine were highly permeable to glucose (% glucose/dextran trap=1.4), whereas glycophorin-containing vesicles prepared from total human erythrocyte lipids demonstrated a greatly reduced permeability in glucose (% glucose/dextran trap=50). (4) The glycophorin-induced increased permeability appears to be related to transbilayer movement of lipid molecules. Glycophorin induces a fast lipid-transbilayer movement of lysophosphatidylcholine and a high permeability to potassium and glucose in dioleoylphosphatidylcholine vesicles, whereas glycophorin-containing vesicles comprised of total human erythrocyte lipids show no lipid-transbilayer movement and only a slight permeability enhancement to glucose, as compared to the protein-free vesicles.