Lithium lowers platelet intracellular ion concentration in bipolar patients

In vitro incubation with lithium significantly lowered platelet free intercellular calcium ion concentration ([Ca²⁺](i)) in untreated bipolar depressed patients but not controls. Platelet [Ca²⁺](i) in bipolars after incubation with lithium, and platelet [Ca²⁺](i) in euthymic patients who had recovered from an episode of bipolar depression and were maintained on lithium, were equivalent to control values. The mechanism of reduction by lithium of platelet [Ca²⁺](i) may involve a specific action on phosphoinositide metabolism or sodium ion homeostasis, or it may be one aspect of a more generalized effect on the cell membrane or a G protein.