Serotonin-Mediated Increase in Cytosolic [Ca⁺⁺] in Platelets of Risperidone-Treated Schizophrenia Patients

Stimulating the platelet 5HT₂ receptor generates the second messenger IPS, 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⁺⁺]_cyt. Data analysis was performed by unpaired two-tailed Student's f-test. No significant differences between groups were found for ED₅₀ 5HT-stimulated [Ca⁺⁺]_cyt (ED₅₀ 5HT Δ [Ca⁺⁺]_cyt). Significant differences were found for maximal change [Ca⁺⁺]_cyt (Max Δ [Ca⁺⁺]_cyt) between risperidone-treated patients and normal controls (p=.03). These preliminary data suggest that measurement of 5HT-stimulated changes in platelet cytosolic [Ca⁺⁺] might be a useful marker for in vivo risperidone inhibition of 5HT₂ function.