LOCALIZED CONTACT FORMATION BY ERYTHROCYTE-MEMBRANES - ELECTROSTATIC EFFECTS

The topology of the contact seam of human erythrocytes adhered by dext ran, an uncharged polymer, has been examined. Particular attention has been paid to the influence of electrostatic intermembrane interaction s since their magnitude and range can be accurately estimated. Normal cells formed a continuous seam, whereas erythrocytes with pronase-modi fied glycocalices formed localized contact points on adhesion in 72 kD a dextran in buffered 145 mM NaCl. The dependence of the inter-contact distance lambda on dextran concentration [D] over the range 2-6% w/v, was given by lambda = C[D]-(0.62), where C was a constant. The index of [D] was independent of dextran molecular mass over the range 20 to 450 kDa. The inter-contact distance for pronase-pretreated cells in 6% w/v 72 kDa dextran increased from 0.78 to 1.4 mu m as [NaCl] was redu ced through the range 145 to 90 mM and the suspending phase was mainta ined at isotonicity by using sorbitol to replace NaCl. The formation a nd lateral separation of the contact points are discussed from the per spective of linear interfacial instability theory. The theory allows a quantitative explanation for the experimentally observed dependence o f inter-contact distance and of disturbance growth rate on change in e lectrostatic interaction. The results suggest that the dominant wavele ngth, determining the inter-contact distance, is established on approa ching membranes when the layers of cell surface charge are separated b y a perpendicular distance of <14 nm (bilayer separation of 24 nm).