Critical Role of the Sodium Hydrogen Exchanger in Maitotoxin-Induced Neuronal Cell Death in Cultured Rat Cortical Neurons

Maitotoxin (MTX) is one of the most potent toxins known to date. It causes massive calcium influx and necrotic cell death in various tissues. However, the exact mechanisms underlying its cellular toxicity are not fully understood. In the present study, the roles of extracellular acidosis and the sodium hydrogen exchanger (NHE) in MTX-induced increase in intracellular Ca and subsequent cell death were investigated in cultured rat cortical neurons. Intracellular Ca ([Ca]i) concentrations were measured fluorimetrically using fura-2 as a fluorescence indicator. Total cell death was measured with the alamarBlue cell viability assay and the vital dye ethidium bromide (EB) uptake assay. Results showed that MTX increased, in a concentration dependent manner, both [Ca]i and cell death in cultured rat cortical neurons. Decreasing the pH of the treatment medium from 7.5 to 6.0 diminished MTX-induced cell death. The protection offered by lowering extracellular pH was not due to MTX degradation, because it was still effective even if the cells were treated with MTX in normal pH and then switched to pH 6.0. Pre-treatment of cells with the specific NHE inhibitor 5-(N-ethyl-Nisopropyl)-amiloride (EIPA) prevented MTX-induced increase in [Ca]i as well as cell death in a concentration dependent manner. These results indicate that NHE is activated by MTX in cultured rat cortical neurons. Because EIPA offered complete protection against MTX-induced cell death, we conclude that NHE plays a major role in MTX neurotoxicity. NHE inhibitors may potentially be used to treat MTX induced neurotoxicity.