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Chapter 9

of MAPKs.214 Additionally, treatment of astrocyte cultures with BAY 11-7082, an inhibitor of NF-kB, reduced cell swelling.214 Similar findings were also observed in astrocyte cultures derived from transgenic mice that have a functional inactivation of astrocytic NF-kB.215 We also found that transgenic mice having a functional inactivation of astrocytic NF-kB did not exhibit brain edema after thioacetamide-induced acute HE.215

While the means by which activation of NF-kB contributes to cell swelling

remains to be determined, it is known that inhibition of NF-kB significantly reduces the activity of inducible nitric oxide synthase,214,216,217 an enzyme implicated in cell swelling mechanisms.214,218,219 Additionally, NF-kB was

found to increase the activity of cyclooxygenase 2 (COX2), and the inhibition of COX2 was shown to reduce cell swelling in cultured retinal Mu¨ller cells.220 Inhibition of NF-kB significantly reduced COX2 activity as well as ammoniainduced astrocyte swelling.218

9.3.9p53

p53 is a tumor suppressor protein and transcription factor that is a key mediator of stress responses.221,222 Activated p53 triggers a number of signaling pathways that may lead to cell cycle arrest, apoptosis and DNA repair.223,224

It also mediates mitochondrial dysfunction, including decreases in the mitochondrial membrane potential and reduction in complex IV activity.225–227 Increased p53 expression was observed in rat brain cytoplasmic extract after

acute ammonia administration.228 It was recently found that astrocyte cultures exposed to ammonia stimulate p53 (phospho-p53ser392) and that treatment of

cultures with pifithrin-a (PFT), an inhibitor of p53, attenuated the ammoniainduced astrocyte swelling.229,230 Additionally, Yan et al. (2008)231 reported

that rats treated with PFT had less brain edema after subarachnoid hemorrhage.

Swelling E ectors

Activation of the above-noted signaling factors ultimately converge on systems that immediately bring about cell swelling. These include various ion channels, exchangers and transporters, as well as the water channel protein aquaporin-4 (AQP-4).

9.3.10Ion Channels/Transporters/Exchangers

Ion channels, exchangers and transporters (ion transporting systems, ITSs) are key factors involved in the maintenance of ionic balance in cells.232–235 These

ITSs include the Na–K–Cl cotransporter (NKCC), volume-sensitive osmolyte anion channels, Na1/Ca21 exchanger, the Na1/H1 exchanger, the SUR1regulated non-selective cation channel (NCCa-ATP) and the transient receptor

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