The platelet intracellular calcium response to serotonin is augmented in bipolar manic and depressed patients

The serotinergic system is widely implicated in the pathophysiology of affective disorder. In this study, basal levels of intracellular calcium as well as the effects of serotonin on intracellular calcium were studied in bipolar manic (N = 21), bipolar depressed (N = 19), bipolar euthymic (N = 20) and normal control (N = 20) subjects. At a serotonin concentration of 100 nm, there was an elevation in intracellular calcium readings, with the highest mean levels in the manic group (158·6, SD = 105·1) followed by the depressed (140·6, SD = 76·4), controls (122·8, SD = 61·6) and the euthymics (96·2, SD = 31·0). The difference between manics and euthymics reached statistcal significance (P = 0·0181) using pooled variance, as did the difference between depressives and euthymics (P = 0·0238). Similar results were found at the 500 nm and 1 μm levels of serotonin. This suggests that an enhanced serotonin mediated mobilization of intracellular calcium occurs in patients in both the manic and depressive phases of bipolar disorder, and may be an index of second messenger dysregulation secondary to hypersensitivity of the platelet 5HT 2 receptor. In addition, the results suggest that this is a state marker of bipolar disorder.