American journal of physiology. Cell physiology
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Am. J. Physiol., Cell Physiol. · Apr 2004
Rat cerebellar granule cells are protected from glutamate-induced excitotoxicity by S-nitrosoglutathione but not glutathione.
In cultured rat cerebellar granule cells, glutamate or N-methyl-d-aspartate (NMDA) activation of the NMDA receptor caused a sustained increase in cytosolic Ca(2+) levels ([Ca(2+)](i)), reactive oxygen species (ROS) generation, and cell death (respective EC(50) values for glutamate were 12, 30, and 38 microM) but no increase in caspase-3 activity. Removal of extracellular Ca(2+) blocked all three glutamate-induced effects, whereas pretreatment with an ROS scavenger inhibited glutamate-induced cell death but had no effect on the [Ca(2+)](i) increase. This indicates that glutamate-induced cell death is attributable to [Ca(2+)](i) increase and ROS generation, and the [Ca(2+)](i) increase precedes ROS generation. ⋯ The transient [Ca(2+)](i) increase and the abolishment of ROS generation induced by glutamate and S-nitrosoglutathione were still seen in the presence of an ROS scavenger. Glial cells, which were present in the cultures used, showed no [Ca(2+)](i) increase in the presence of glutamate, and glutamate-induced granule cell death was independent of the percentage of glial cells. In conclusion, NO donors protect cultured cerebellar granule cells from glutamate-induced cell death, which is mediated by ROS generated by a sustained [Ca(2+)](i) increase, and glial cells provide negligible protection against glutamate-induced excitotoxicity.
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Am. J. Physiol., Cell Physiol. · Apr 2004
Oxidative stress decreases pHi and Na(+)/H(+) exchange and increases excitability of solitary complex neurons from rat brain slices.
Putative chemoreceptors in the solitary complex (SC) are sensitive to hypercapnia and oxidative stress. We tested the hypothesis that oxidative stress stimulates SC neurons by a mechanism independent of intracellular pH (pH(i)). pH(i) was measured by using ratiometric fluorescence imaging microscopy, utilizing either the pH-sensitive fluorescent dye BCECF or, during whole cell recordings, pyranine in SC neurons in brain stem slices from rat pups. Oxidative stress decreased pH(i) in 270 of 436 (62%) SC neurons tested. ⋯ CT increased firing rate in 14 of 16 SC neurons, and there was no difference in the firing rate response to CT with or without a corresponding change in pH(i). These results indicate that oxidative stress 1). decreases pH(i) in some SC neurons, 2). together with hypercapnia has an additive effect on pH(i), 3). partially inhibits NHE, and 4) directly affects excitability of CO(2)/H(+)-chemosensitive SC neurons independently of pH(i) changes. These findings suggest that oxidative stress acidifies SC neurons in part by inhibiting NHE, and this acidification may contribute ultimately to respiratory control dysfunction.