Effects of lithium on platelet ionic intracellular calcium concentration in patients with bipolar (manic-depressive) disorder and healthy controls

Lithium is an effective drug in the treatment of both manic and depressive episodes of bipolar disorder. Lithium has been shown to block the metabolism of the intracellular second messenger inositol-1,4,5-trisphosphate which is involved in the rise in ionic intracellular calcium ([Ca⁺⁺]_i) which triggers neurotransmitter release and other cellular changes in secretory cells. We have measured the effect of lithium on [Ca⁺⁺]_i dynamics in platelets from bipolar patients stabilized with lithium treatment, and from healthy controls. Both resting [Ca⁺⁺]_i and the thrombin stimulated increase in [Ca⁺⁺]_i were higher in bipolar patients than in controls. Lithium added in vitro tended to increase the thrombin-stimulated rise in [Ca⁺⁺]_i. The use of the fluorescent Ca⁺⁺ probe fura-2 in human platelets provides a useful method to investigate the mechanism of lithium's action in bipolar disorder and to study Ca⁺⁺ related systems which may be abnormal in bipolar disorders.