Na ⁺ /H ⁺ Exchanger Inhibitor, SM-20220, Is Protective Against Excitotoxicity in Cultured Cortical Neurons

Abstract

Background and Purpose-Recently, it has been reported that Na ϩ /H ϩ exchanger (NHE) inhibitors demonstrated protective effects on ischemia/reperfusion brain injury in animal models. However, the mechanisms by which the neurons were protected against ischemic insult remain unclear. To reveal the cellular mechanism of the NHE inhibitor on the neuronal death, we examined the effects of a selective NHE inhibitor, SM-20220 (N-[aminoiminomethyl]-1-methyl-1H-indole-2-carboxamide methanesulfonate), on glutamate-induced neuronal death in rat cortical culture. Methods-Cortical neurons were prepared from 1-day old rats, and cultured on the glass-based dishes. Glutamate-induced neuronal death was assessed by staining the cells with propidium iodide. Morphological changes in the neurons were observed with a video-enhanced contrast-differential interference contrast microscope. The intracellular calcium concentration ([Ca 2ϩ ] i ) and the intracellular pH (pH i ) were measured by fluorescence imaging with a confocal laser microscope using fluo-3/acetoxymethylester (AM) and 2Ј, 7Ј-bis-2-carboxy-ethyl-5(6)-carboxyfluorescein (BCECF)/AM as a fluorescent dye, respectively.

Effects of sabiporide, a specific Na+/H+ exchanger inhibitor, on neuronal cell death and brain ischemia

“…3). Considering that the activation of glutamate receptors is one of the characteristics during various brain damages including stroke, these results support the previous studies suggesting that the NHE inhibitor may be a potential neuroprotective agent against brain ischemic disease [14]. It is well known that Ca 2+ overload plays a crucial role for brain ischemic injuries [7].…”

“…Therefore, it is highly conceivable that the inhibition of NHE contributes to prevent the intracellular Ca 2+ increase and subsequent excitotoxic neuronal death. Indeed, it has been shown that the protective effects of NHE inhibitors are in good correlation with the intracellular Ca 2+ lowering effect associated with NHE inhibition in various cardiac [13] and brain ischemia model [14]. We, therefore, investigated whether the neuroprotective effect of sabiporide is associated with the inhibition of intracellular Ca 2+ overload induced by excitotoxicity.…”

Intracellular Acidification Is Associated with Changes in Free Cytosolic Calcium and Inhibition of Action Potentials in Rat Trigeminal Ganglion

“…Many biological processes, such as enzyme activity, ionic conductance, and activity of membrane transporters, are pH-sensitive (3,4). Thus, the regulation of pH i in neurons is of critical importance; failure to maintain pH i may lead to numerous pathophysiological conditions (5,6). Neurons may become acidified in response to neurotransmitters and chemical compounds (7)(8)(9), and this intracellular acidification has been linked to the activity of the plasma membrane Ca 2ϩ /ATPase (PMCA) (10,11).…”

KR-33028, a Novel Na+/H+Exchanger-1 Inhibitor, Attenuates Glutamate-Induced Apoptotic Cell Death through Maintaining Mitochondrial Function

“…Glutamate excitotoxicity was triggered by entry of extracellular Ca 2+ through activation of NMDA receptor of ionotropic glutamate (Choi, 1988). The increase in intracellular Ca 2+ leads to a cascade of events, which can precipitate necrosis and/or apoptosis of susceptible neurons (Matsumoto et al, 2004). The increase in cytosolic Ca 2+ is associated with mitochondrial Ca 2+ loading and slight mitochondrial depolarization followed by profound depolarization concurrent with the loss of ionic homeostasis (Hans et al, 2005).…”

“…+ /H + exchange-1 (NHE-1) is activated by intracellular acidifi cation, leading to Na + uptake from the extracellular medium and extrusion of intracellular H + (Trudeau et al, 1999). However, excessive activation of NHE-1 during glutamate excitotoxocity leads to remarkable elevation of intracellular Na + , and then the increase in Na + infl ux reverses the Na + /Ca 2+ exchange (NCX) system to protrude Na + , subsequently causing intracellular Ca 2+ overload (Matsumoto et al, 2004). Recent investigations on neuronal tissue culture and an animal ischemia model suggested that the blockage of NHE-1 may protect ischemic brain tissue possibly by preventing intracellular Ca 2+ entry due to NHE-1 inhibition (Glunde et al, 2002).…”