The effect of lithium on the membrane molecular dynamics of normal human erythrocytes

Erythrocytes from normal adults with no personal or family history of bipolar affective disorder were analyzed by fluorescence spectroscopy to determine what effect, if any, acute in vitro incubation with lithium had on erythrocyte membrane dynamics. The effects on erythrocyte membrane molecular dynamics of varying concentrations of Li2CO3 (0.25-2.0 meq/liter), varying incubation temperatures (25-40 degrees C), and varying incubation times (5-185 min) were investigated. Following incubation with Li2CO3, the erythrocytes were labeled with either 4-phenylspiro-[furan-2(3H),--1'phthalan]--3,3'-dione (fluorescamine), which binds to membrane surface primary amines, or 12(9)anthroyl stearate [12(9)AS], which inserts deep in the membrane hydrocarbon core. The membrane molecular dynamics were then determined by fluorescence anisotropy measurements. These studies demonstrate that clinically relevant concentrations of Li+ incubated with intact normal human erythrocytes significantly alters molecular dynamics on the erythrocyte membrane surface, with less striking changes in the hydrocarbon core. A possible interpretation of these findings is that hydrated Li+ alters the electrostatic interaction of membrane surface molecules, as well as the surrounding solvent (water) structure, with a resultant increase in the molecular motion of these molecules. Alterations in membrane receptor motion could potentially alter receptor functional activity. If similar motional alterations were to occur in the interior of a membrane channel, such as an ionophore, the functional activity of the channel could also be potentially altered. These findings provide additional insight into possible biological actions of Li+, as well as potential molecular alterations in bipolar affective disorder erythrocytes.