Serotonin-mediated increase in cytosolic [Ca++] in platelets of risperidone-treated schizophrenia patients

Stimulating the platelet 5HT2 receptor generates the second messenger IP3, and results in an increase in cytosolic [Ca++] ([Ca++]cyt). Platelets from risperidone-treated patients would be expected to respond less effectively, as measured by decreased [Ca++]cyt, after 5HT2 receptor stimulation. We report the data on 6 risperidone-treated patients and 6 normal controls evaluated at our site using the Fura-2 method for determining platelet [Ca++]. Data analysis was performed by unpaired two-tailed Student's t-test. No significant differences between groups were found for ED50 5HT-stimulated [Ca++]cyt (ED50 5HT delta [Ca++]cyt). Significant differences were found for maximal change [Ca++]cyt (Max delta [Ca+2]cyt) between risperidone-treated patients and normal controls (p = .03). These preliminary data suggest that measurement of 5HT-stimulated changes in platelet cytosolic [Ca+2] might be a useful marker for in vivo risperidone inhibition of 5HT2 function.