Altered platelet serotonin uptake kinetics in schizophrenia and depression

Platelet uptake of serotonin (5-HT) was studied in drug-free groups of normal controls, depressives and schizophrenics. The Michaelis constant was significantly higher in both the schizophrenics and the depressives than in the controls. The V_max did not differ significantly between the three groups. Uptake velocity at low substrate concentrations was significantly lower in the schizophrenic group and showed a similar trend in the depressives. There were no significant differences in K_m or V_max when depressives were subclassified as unipolar and bipolar. There were no significant correlations between 5-HT uptake kinetics and severity of illness. These findings raise the possibility of a structural defect in the 5-HT reuptake system in the major psychoses that reduces the affinity of the carrier for the amine. This alteration, if present in central serotonergic neurons, may play a role in the etiology and pathogenesis of depression and schizophrenia.