Chronic administration of lithium modulates tryptophan transport by changing the properties of the synaptosomal plasma membrane.

The effect of chronic administration of lithium salts on the sodium dependent high-affinity system for tryptophan uptake was examined in plasma membrane vesicles derived from rat brain. Tryptophan transport was measured as a function of the temperature, Arrhenius plots of the data were prepared, and the apparent energies of activation were computed. Both plots were biphasic, the transition temperature decreasing from 23 degrees C in control animals to 18 degrees C in treated rats. The average apparent energies of activation for the carrier also change -both below and above the transition temperature- in treated animals when compared to controls. Our data support the idea that chronic administration of lithium induces a more fluid state of the synaptosomal plasma membrane that could explain many of the effects of Li+ on membrane-bound proteins.