Coordinated role of voltage-gated sodium channels and the Na+/H+ exchanger in sustaining microglial activation during inflammation

Persistent neuroinflammation and microglial activation play an integral role in the pathogenesis of many neurological disorders. We investigated the role of voltage-gated sodium channels (VGSC) and Na+/H+ exchangers (NHE) in the activation of immortalized microglial cells (BV-2) after lipopolysaccharide (LPS) exposure. LPS (10 and 100 ng/ml) caused a dose- and time-dependent accumulation of intracellular sodium [(Na+)i] in BV-2 cells. Pre-treatment of cells with the VGSC antagonist tetrodotoxin (TTX, 1 μM) abolished short-term Na+ influx, but was unable to prevent the accumulation of (Na+)i observed at 6 and 24 h after LPS exposure. The NHE inhibitor cariporide (1 μM) significantly reduced accumulation of (Na+)i 6 and 24 h after LPS exposure. Furthermore, LPS increased the mRNA expression and protein level of NHE-1 in a dose- and time-dependent manner, which was significantly reduced after co-treatment with TTX and/or cariporide. LPS increased production of TNF-α, ROS, and H2O2 and expression of gp91phox, an active subunit of NADPH oxidase, in a dose- and time-dependent manner, which was significantly reduced by TTX or TTX + cariporide. Collectively, these data demonstrate a closely-linked temporal relationship between VGSC and NHE-1 in regulating function in activated microglia, which may provide avenues for therapeutic interventions aimed at reducing neuroinflammation.