PLATELET AND LYMPHOCYTE FREE INTRACELLULAR CALCIUM IN AFFECTIVE-DISORDERS

Many studies have demonstrated pharmacologic similarities between plat elet and brain 5-HT2 binding sites. Therefore it may be possible to us e platelets as a model for the central serotonergic neuron. Accordingl y, a previous report (Kusumi et al. 1991b) about elevated [Ca2+](i) af ter serotonin stimulation in platelets of depressed patients was inter preted as further evidence for enhanced serotonergic sensitivity in de pression. However, a very recent study showed an enhanced thrombin-ind uced platelet Ca2+ response, rather suggesting abnormalities of intrac ellular Ca2+ regulation in affective disorders. In the present study w e have determined 5-HT2- and thrombin-induced Ca2+ responses in platel ets and additionally phytohemagglutin (PHA)-induced Ca2+ increase in l ymphocytes of medicated depressed patients (8 mono- and 2 bipolar, HRS D > 17) and of ten sex- and age-matched controls. The results showed n o significant difference in basal calcium levels between the two group s and no significant difference in the Ca2+ response to thrombin altho ugh the response was higher in the patients. The Ca2+ increase after s erotonin stimulation in depressed patients was significantly (P < 0.05 ) higher than in healthy controls. By contrast, the Ca2+ response to P HA in lymphocytes was significantly decreased in the patients. Our dat a confirm elevated Ca2+ responses after 5-HT2 receptor activation even in medicated depressed patients. However, Ca2+ responses in lymphocyt es were decreased. Together with the observations of an enhanced Ca2response in platelets after thrombin stimulation, we speculate that th e findings rather suggest alterations of [Ca2+](i) regulation in depre ssion than specific changes of serotonergic sensitivity.