Membrane hyperpolarization following chronic exposure of FL-cells to low doses of ouabain.

The transmembrane potential (TMP) of FL-cells (monolayer cultures) in Eagle's medium with ouabain concentrations from 10(-4) to 10(-11) M was measured by means of glass microelectrodes over 96 h. High ouabain concentrations caused total depolarization of the cell membrane with subsequent cell death after 24 to 48 h. A level of 10(-7) M ouabain was tolerated by the cells over 96 h, and the TMP was decreased about 50% vs. controls in ouabain-free medium. Ouabain at concentrations from 10(-11) to 10(-8) M increases TMP by 20-40%, which decayed after 24 to 48 h. The low glycoside concentrations are assumed to cause, if only part of the glycoside receptors (Na+ pumps) is blocked, an activation of the still active pumps (turnover) and enhanced formation of transport enzymes and their incorporation into the membrane (replacement) so that the overall result is a stimulation of the cell membrane transport systems.