Chloroquine inhibits Ca(2+) permeable ion channels-mediated Ca(2+) signaling in primary B lymphocytes

BACKGROUND: Chloroquine, a bitter tastant, inhibits Ca(2+) signaling, resulting in suppression of B cell activation; however, the inhibitory mechanism remains unclear. RESULTS: In this study, thapsigargin (TG), but not caffeine, induced sustained intracellular Ca(2+) increases in mouse splenic primary B lymphocytes, which were markedly inhibited by chloroquine. Under Ca(2+)-free conditions, TG elicited transient Ca(2+) increases, which additionally elevated upon the restoration of 2 mM Ca(2+). The former were from release of intracellular Ca(2+) store and the latter from Ca(2+) influx. TG-induced release was inhibited by 2-APB (an inhibitor of inositol-3-phosphate receptors, IP(3)Rs) and chloroquine, and TG-caused influx was inhibited by pyrazole (Pyr3, an inhibitor of transient receptor potential C3 (TRPC3) and stromal interaction molecule (STIM)/Orai channels) and chloroquine. Moreover, chloroquine also blocked Ca(2+) increases induced by the engagement of B cell receptor (BCR) with anti-IgM. CONCLUSIONS: These results indicate that chloroquine inhibits Ca(2+) elevations in splenic B cells through inhibiting Ca(2+) permeable IP(3)R and TRPC3 and/or STIM/Orai channels. These findings suggest that chloroquine would be a potent immunosuppressant.