SEA0400, a specific inhibitor of the Na+–Ca2+ exchanger, attenuates sodium nitroprusside‐induced apoptosis in cultured rat microglia

1 Using SEA0400, a potent and selective inhibitor of the Na+–Ca2+ exchanger (NCX), we examined whether NCX is involved in nitric oxide (NO)-induced disturbance of endoplasmic reticulum (ER) Ca2+ homeostasis followed by apoptosis in cultured rat microglia. 2 Sodium nitroprusside (SNP), an NO donor, decreased cell viability in a dose- and time-dependent manner with apoptotic cell death in cultured microglia. 3 Treatment with SNP decreased the ER Ca2+ levels as evaluated by measuring the increase in cytosolic Ca2+ level induced by exposing cells to thapsigargin, an irreversible inhibitor of ER Ca2+-ATPase. 4 The treatment with SNP also increased mRNA expression of CHOP and GPR78, makers of ER stress. 5 SEA0400 at 0.3–1.0 μM protected microglia against SNP-induced apoptosis. 6 SEA0400 blocked not only the SNP-induced decrease in ER Ca2+ levels but also SNP-induced increase in CHOP and GRP78 mRNAs. 7 SEA0400 did not affect capacitative Ca2+ entry in the presence and absence of SNP. 8 SNP increased Na+-dependent 45Ca2+ uptake and this increase was blocked by SEA0400. 9 These results suggest that SNP induces apoptosis via the ER stress pathway and SEA0400 attenuates SNP-induced apoptosis via suppression of the ER stress in cultured microglia. Our findings imply that NCX plays a role in ER Ca2+ depletion under pathological conditions. British Journal of Pharmacology (2005) 144, 669–679. doi:10.1038/sj.bjp.0706104