[Changes in the kinetics of erythrocyte membrane transport of tryptophan in depression].
The initial rate of L-tryptophan uptake into human red cells as a function of its concentration in the medium was measured in a group of 8 depressed patients hospitalized included 2 bipolar disorders (296.5x, DSM III), 3 major depressions, single episode or recurrent (296.3x and 296.2x, DSM III) and 3 dysthymic disorders (300.40x, DSM III), which were out of antidepressive treatment, with age ranging from 34 to 64 years compared to a group of 11 healthy volunteers with age ranging from 23 to 54 ans. Kinetic constants were measured at 37 degrees C on red cells incubated with tritiated L-tryptophan and cold L-tryptophan over the concentration range 0.1 to 10 mM. The maximum velocity (Vmax) of the saturable transport is severely lowered in a significant manner in the patients compared to controls (mean +/- s.e.m. = 48.9 +/- 5.5 mumol/l cells/min and 92.0 +/- 14 which represents 47% in decrease). In return, the Michaelis constant is unaffected. The linear component of tryptophan transport, which corresponds to the participation of nonspecific transport systems, is not modified. The possible incidence of such a deficit in the plasmatic reserve of tryptophan in depressed patients on the central availability of serotonin synthesis precursor is postulated.