Regulation by sulfanylurea receptor type 1 of a non-selective cation channel involved in cytotoxic edema of reactive astrocytes.
Hypoxia-ischemia and ATP depletion are associated with cytotoxic edema of glial cells, but mechanisms involved remain incompletely characterized. We examined morphologic and electrophysiological responses of freshly isolated native reactive astrocytes (NRAs) following exposure to NaN3, which depletes cellular ATP. NaN3 caused profound and sustained depolarization due to activation of a novel 35 pS Ca2+-activated, [ATP]i-sensitive non-selective cation (NCCa-ATP) channel found in >90% of excised membrane patches. This channel exhibited significantly different properties compared with previously reported NCCa-ATP channels, including different sensitivity to block by various adenine nucleotides (EC50=0.79 microM for [ATP]i, with no block by AMP or ADP), and activation by submicromolar [Ca]i. In addition, the channel was found to be regulated in a manner identical to that of SUR1-regulated KATP channels, including high affinity block by glybenclamide and tolbutamide, and opening by diazoxide. mRNA transcription and protein expression of SUR1 but not SUR2 were confirmed in reactive astrocytes both in situ and after isolation, whereas Kir6.x, which forms the pore-forming subunit of the KATP channel, was not expressed. Channel opening by [ATP]i depletion or exposure to diazoxide caused blebbing of the cell membrane, whereas [ATP]i depletion in the presence of glybenclamide did not. These findings are consistent with participation of this channel in cation flux involved in cell swelling. This novel channel may play an important role in the pathogenesis of brain swelling.
Simard
J Marc
JM
Department of Neurosurgery, University of Maryland School of Medicine, Baltimore, MD 21201, USA. msimard@smail.umaryland.edu
Chen
Mingkui
M
D018528:ATP-Binding Cassette Transporters / Q000494:pharmacology / Q000502:physiology*; D000328:Adult; D001253:Astrocytes / Q000187:drug effects* / Q000648:ultrastructure; D001929:Brain Edema / Q000503:physiopathology / Q000517:prevention & control*; D002412:Cations / Q000378:metabolism*; D002469:Cell Separation; D006801:Humans; D007473:Ion Channels / Q000187:drug effects*; D008855:Microscopy, Electron, Scanning; D009153:Mutagens / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000494:pharmacology / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug / Q000502:physiology*; D019810:Sodium Azide / Q000494:pharmacology*; D064233:Sulfonylurea Receptors
C577507:ABCC8 protein, human; C577510:ABCC9 protein, human; D018528:ATP-Binding Cassette Transporters; D002412:Cations; D007473:Ion Channels; D009153:Mutagens; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; D019810:Sodium Azide