SEA0400 is a selective inhibitor of the Na+/Ca2+ exchanger.

SEA0400 inhibits Na+-dependent 45Ca2+ uptake in cultured neurons, astrocytes, and microglia. IC50 values of SEA0400 are 33 nM (neurons), 5.0 nM (astrocytes), and 8.3 nM (microglia)[1]. SEA0400 prevents sodium nitroprusside (SNP) to increase ERK and p38 MAPK phosphorylation, and production of reactive oxygen species (ROS) in an extracellular Ca2+-dependent manner[2].

SEA0400, administered intravenously at a dose of 3 mg/kg followed by 3 mg/kg/h for 2 hours, reduces infarct volume in the cerebral cortex and striatum without altering mean regional cortical blood flow in anesthetized rats[1]. Additionally, SEA0400 offers protection against dopaminergic neurotoxicity, as evidenced by maintained dopamine levels in the midbrain and striatum, preserved tyrosine hydroxylase immunoreactivity in the substantia nigra and striatum, normal striatal dopamine release, and avoidance of motor deficits in MPTP-treated C57BL/6J mice[3].

Na+-Ca2+ exchange activity is determined by assaying Na+-dependent 45Ca2+ uptake as reported previously. Briefly, the cells are preincubated in Hanks' balanced saline solution (HBSS) for 20 min, and the medium is switched to HBSS containing 45Ca2+?and incubated for 5 min. To increase intracellular Na+?concentration, 1 mM ouabain plus 20 μM monensin (for astrocytes and microglia) and 10 μM monensin (for neurons) are used. Monensin is added simultaneously with the isotope. Ouabain is added 5 min before monensin in astrocytes and microglia. SEA0400 and KB-R7943 are added 5 min before monensin and present during 45Ca2+?uptake reaction.

SEA0400 is dissolved in DMSO (final concentration 0.1%). Cells, plated in 96-well plastic tissue culture plates, are incubated at 37°C for 30 min in normal or Ca2+-free HBSS containing 10 μM H2DCF-DA and 0.25 μg/mL Cremophor EL, and then rinsed twice with normal HBSS to remove excess dye. The cells are reperfused in normal HBSS for 1 h, and the conversion of H2DCF-DA to its fluorescent product dichlorofluorescein by ROS, presumably Water2 and hydroxyl radical, is determined with excitation at 485 nm and emission at 535 nm using a Wallac Multilabel counter. ROS production is expressed as a percentage of control cells. The linearity and sensitivity of ROS assay are confirmed using Water2 prior to the experiment. SEA0400 at the indicated concentrations is added 10 min before Ca2+?reperfusion and present until assay.