Alterations in the electrical properties of T and B lymphocyte membranes induced by mitogenic stimulation. Activation monitored by electro-rotation of single cells.

Stimulation of either B or T lymphocytes using specific mitogens results in changes in the passive electrical properties of the cell surface. These effects can be related to growth and secretion. This was possible because the high resolution of the contra-field electro-rotation method, combined with the use of very low conductivity media, allowed accurate and analytically-derived values for the cell surface properties. Increases in effective CM (membrane capacity) and changes in apparent membrane conductivity (reflecting the additive effects of true membrane conductivity GM and surface conductance KS) were measured. After 72 h treatment with concanavalin A, thymocyte CM had increased from 0.76 muF/cm2 to 1.24-1.46 muF/cm2 (7.6 to 12.4-14.6 mF/m2). Allowing for the stimulation-induced size increase (cell radius increased from 2.8 to 4.4 micron) these data imply that the plasma membrane area per cell increases 5-fold during stimulation. Stimulation of B cells (by 3 days incubation with bacterial lipopolysaccharide) increased CM from 0.93 to 1.6-1.7 muF/cm2 (9.3 to 16-17 mF/m2). Incubation without mitogen gave no significant increase in CM or in radius. Control cells of different sizes showed no difference in membrane properties. The increases in effective CM are argued to reflect an increase in membrane ramification (microvilli, folding, etc.). The apparent membrane conductivity of T cells also increased during stimulation, from 5 to 21 mS/cm2 (50 to 210 S/m2). This increase is proportionately much greater than that in CM or in membrane area. It seems to be due to a real increase in GM, but a small increase in KS may also occur. The earliest changes in apparent membrane conductivity were evident between 3 and 5 h after stimulation, before the cells increased in size. This response parallels increases in transmembrane transport reported to follow mitogenic stimulation.