Intracellular calcium concentrations ([Ca++]i) in blood platelets from 11 depressed patients and 11 healthy controls were investigated. The resting [Ca++]i of platelets from depressed patients was 69.4±2.9 nM while that from controls was 74.6±4.0 nM. Serotonin (5-HT), at a concentration of 10 μM, increased [Ca++]i by 129.2±3.9 nM in platelets from depressed patients, which was significantly greater than that found in platelets from control subjects (105.2±6.0 nM). Norepinephrine (NE) 100 μM increased [Ca++]i by 46.1±7.1 nM in platelets from depressed patients, and by 38.6±6.1 nM in platelets from controls, respectively. These results indicate that 5-HT2 receptor function in platelets of depressed patients is enhanced, and support the hypothesis of hypersensitivity of 5-HT2 receptors in affective disorders.
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