Increased platelet intracellular calcium ion concentration is specific to bipolar disorder

Background Increased baseline ([Ca²⁺]_B) and agonist-stimulated ([Ca²⁺]_s) free intracellular calcium ion concentrations ([Ca²⁺]_i) are well-replicated findings in bipolar disorder, but whether this finding is specific to that condition and if so, whether it is a marker of the mood disorder or a feature seen in other disorders such as psychosis has remained unclear. Methods Platelet [Ca ²⁺]_i was assessed in 15 inpatients with psychotic and nonpsychotic mania, 17 schizophrenia inpatients, and 17 matched controls. Results Platelet [Ca²⁺]_B and [Ca²⁺]_s were significantly higher than controls in bipolar disorder but not schizophrenia. Variability of [Ca²⁺]_B was significantly increased in bipolar disorder regardless of the presence of psychosis, but not in schizophrenia. Limitations Use of antipsychotic drugs by the majority of both patient groups may have obscured elevated [Ca²⁺]_i in schizophrenia, or may have masked a difference between psychotic and nonpsychotic bipolar disorder. Measurement of [Ca²⁺]_i is too labor intensive to become a routine test for diagnosis or prediction of treatment response. Conclusions Elevated intracellular Ca²⁺ signaling may be a marker of primary cellular hyperactivity that could contribute to comorbid conditions such as hypertension and neuronal apoptosis. Since lithium and carbamazepine attenuate increased [Ca²⁺]_i, further research may demonstrate a correlation between normalization of [Ca ²⁺]_i and response to one of these medications, and further research may clarify whether a subgroup of patients may respond well to calcium channel antagonists.