Serotonin-induced platelet intracellular Ca2+ responses in untreated depressed patients and imipramine responders in remission

Background: Intracellular Ca2+ metabolism in platelets has been investigated as a peripheral marker of affective disorders. Methods: We investigated the intracellular free Ca2+ concentration in platelets in both untreated depressed patients with no medications and patients in remission who were treated by imipramine (IMI) (IMI responders) using a Ca2+-sensitive fluorescent probe fura-2. Results: The increases in intracellular free Ca2+ concentration in platelets induced by stimulation with serotonin (5-HT) ([Ca2+]Δ) were significantly higher in both the untreated patients and the IMI responders compared with healthy controls; however, there were no significant differences in the basal Ca2+ levels in the platelets ([Ca2+]B) among the three groups. On the other hand, in the IMI responders, we observed positive correlations between the duration of the remission and [Ca2+]B, but not [Ca2+]Δ. Conclusions: Our present data suggest that the enhancement of 5-HT2A-induced Ca2+ responses persisted after remission in depressed patients, and that the duration of the remission is a factor varying the intracellular