Role of Plasma Membrane at Dielectric Relaxations and Intermembrane Interaction in Human Erythrocytes

Dielectric relaxations at 1.4 MHz (β(sp)) and 9 MHz (γ1(sp)) on the erythrocyte spectrin network were studied by dielectric spectroscopy using dense suspensions of erythrocytes and erythrocyte ghost membranes, subjected to extraction with up to 0.2% volume Triton-X-100. The step-wise extraction of up to 60% of membrane lipids preserved γ1(sp) and gradually removed β(sp)-relaxation. On increasing the concentration up to 100 mM of NaCl at either side of erythrocyte plasma membranes, the β(sp)-relaxation was linearly enhanced, while the strength of γ1(sp)-relaxation remained unchanged. In media with NaCl between 100 and 150 mM β(sp)-relaxation became slightly inhibited, while γ1(sp)-relaxation almost disappeared, possibly due to the decreased electrostatic repulsion allowing erythrocytes to come into closer contact. When these media contained, at concentrations 10–30 mg/mL dextran (MW 7 kDa), polyethylene glycol or polyvinylpyrrolidone (40 kDa), or albumin or homologous plasma with equivalent concentration of albumin, the γ1(sp)-relaxation was about tenfold enhanced, while β(sp)-relaxation was strengthened or preserved. The results suggest the Maxwell–Vagner accumulation of ions on the lipid bilayer as an energy source for β(sp)-relaxation. While β(sp)-relaxation appears sensitive to erythrocyte membrane deformability, γ1(sp)-relaxation could be a sensitive marker for the inter-membrane interactions between erythrocytes.