Chronic lithium treatment attenuates intracellular calcium mobilization

Elevated basal intracellular calcium (Ca2+) levels ([Ca2+](B)) in B lymphoblast cell lines (BLCLs) from bipolar I disorder (BD-I) patients implicate altered Ca2+ homeostasis in this illness. Chronic lithium treatment affects key proteins modulating intracellular Ca2+ signaling. Thus, we sought to determine if chronic exposure to therapeutic lithium concentrations also modifies intracellular Ca2+ homeostasis in this surrogate cellular model of signal transduction disturbances in BD. BLCLs from BD-I (N=26) and healthy subjects (N=17) were regrown from frozen stock and incubated with 0.75 mM lithium or vehicle for 24 h (acute) or 7 days (chronic). [Ca2+](B), lysophosphatidic acid (LPA)-stimulated Ca2+ mobilization ([Ca2+](S)), and thapsigargin-induced store-operated Ca2+ entry (SOCE) were determined using ratiometric fluorometry with Fura-2. Compared with vehicle, chronic lithium exposure resulted in significantly higher [Ca2+](B) (F=8.47; p=0.006) in BLCLs from BD-I and healthy subjects. However, peak LPA-stimulated [Ca2+](S) and SOCE were significantly reduced (F=11.1, p=0.002 and F=8.36, p=0.007, respectively). Acute lithium exposure did not significantly affect measured parameters. In summary, the effect of chronic lithium to elevate [Ca2+](B) in BLCLs while attenuating both receptor-stimulated and SOCE components of intracellular Ca2+ mobilization in BLCLs suggests that modulation of intracellular Ca2+ homeostasis may be important to the therapeutic action of lithium.