Focal cerebral ischaemia and post-ischaemic reperfusion cause cerebral capillary dysfunction, resulting in oedema formation and haemorrhagic conversion. There are substantial gaps in understanding the pathophysiology, especially regarding early molecular participants. Here, we review physiological and molecular mechanisms involved. We reaffirm the central role of Starling's principle, which states that oedema formation is determined by the driving force and the capillary "permeability pore". We emphasise that the movement of fluids is largely driven without new expenditure of energy by the ischaemic brain. We organise the progressive changes in osmotic and hydrostatic conductivity of abnormal capillaries into three phases: formation of ionic oedema, formation of vasogenic oedema, and catastrophic failure with haemorrhagic conversion. We suggest a new theory suggesting that ischaemia-induced capillary dysfunction can be attributed to de novo synthesis of a specific ensemble of proteins that determine osmotic and hydraulic conductivity in Starling's equation, and whose expression is driven by a distinct transcriptional program.Correspondence to: Dr J Marc Simard, Department of Neurosurgery, 22 S. Greene St., Suite 12SD, Baltimore, MD 21201−1595, USA msimard@smail.umaryland.edu. Contributors JMS originated the overall concept for this review and wrote the first and second drafts. TAK contributed to and helped edit the first and second drafts, and supplied important citations. MC participated in the original work on the sections on the NC Ca-ATP channel and contributed to the first draft. KVT did the computer analysis of the gene promoter regions. VG engaged in numerous intellectual exchanges with JMS during formulation of concepts for this review.Conflict of interest JMS and MC have applied for a US patent, "A novel non-selective cation channel in neural cells and methods for treating brain swelling" (application number 10/391,561). NIH Public Access

Pathological conditions in the central nervous system, including stroke and trauma, are often exacerbated by cerebral edema. We recently identified a nonselective cation channel, the NC Ca-ATP channel, in ischemic astrocytes that is regulated by sulfonylurea receptor 1 (SUR1), is opened by depletion of ATP and, when opened, causes cytotoxic edema. Here, we evaluated involvement of this channel in rodent models of stroke. SUR1 protein and mRNA were newly expressed in ischemic neurons, astrocytes and capillaries. Upregulation of SUR1 was linked to activation of the transcription factor Sp1 and was associated with expression of functional NC Ca-ATP but not K ATP channels. Block of SUR1 with low-dose glibenclamide reduced cerebral edema, infarct volume and mortality by 50%, with the reduction in infarct volume being associated with cortical sparing. Our findings indicate that the NC Ca-ATP channel is crucially involved in development of cerebral edema, and that targeting SUR1 may provide a new therapeutic approach to stroke.Edema complicates many conditions that affect the central nervous system (CNS), including stroke and trauma. Edema worsens neurological function and can threaten life. Swelling resulting from malignant cerebral edema after a large middle cerebral artery (MCA) stroke is responsible for the high mortality of 60−80% of the patients 1 . Molecular mechanisms of cerebral edema are poorly understood, and available treatments are nonspecific and only moderately effective 1 .SUR1 is a regulatory subunit that associates with Kir6.x pore-forming subunits to form heterooctameric K ATP channels 2 . SUR1 confers sensitivity to sulfonylurea inhibitors such as glibenclamide and to channel activators such as diazoxide. Apart from involvement with

We previously identified a novel, nonselective cation channel in native reactive (type R1) astrocytes (NR1As) from injured rat brain that is regulated by cytoplasmic Ca2+ and ATP (NC(Ca-ATP)) and exhibits sensitivity to block by adenine nucleotides similar to that of sulfonylurea receptor type 1 (SUR1). Here we show that SUR1 is involved in regulation of this channel. NR1As within the site of injury and after isolation exhibited specific binding of FITC-tagged glibenclamide and were immunolabeled with anti-SUR1 antibody, but not with anti-SUR2, anti-Kir6.1 or anti-Kir6.2 antibodies, indicating absence of ATP-sensitive K+ (KATP) channels. RT-PCR confirmed transcription of mRNA for SUR1 but not SUR2. Several properties previously associated exclusively with SUR1-regulated KATP channels were observed in patch-clamp experiments using Cs+ as the charge carrier: (1) the sulfonylureas, glibenclamide and tolbutamide, inhibited NCCa-ATP channels with EC50 values of 48 nm and 16.1 microm, respectively; (2) inhibition by sulfonylureas was lost after exposure of the intracellular face to trypsin or anti-SUR1 antibody; (3) channel inhibition was caused by a change in kinetics of channel closing, with no change in channel amplitude or open-channel dwell times; and (4) the SUR activator ("KATP channel opener"), diazoxide, activated the NCCa-ATP channel, whereas pinacidil and cromakalin did not. Also, glibenclamide prevented cell blebbing after ATP depletion, whereas blebbing was produced by exposure to diazoxide. Our data indicate that SUR1 is functionally coupled to the pore-forming portion of the NC(Ca-ATP) channel, providing the first demonstration of promiscuity of SUR1 outside of the K+ inward rectifier family of channels.

The multifunctional cytokine, transforming growth factor ␤ 1 (TGF-␤ 1 ), exerts complex effects on astrocytes with early signaling events being less well characterized than transcriptional mechanisms. We examined the effect of TGF-␤ 1 on the 14-pS Kir2.3 inward rectifier K ؉ channel in rat primary cultured reactive astrocytes. Immunofluorescence study showed that cells co-expressed TGF-␤ 1 receptors 1 and 2, Kir2.3, and glial fibrillary acidic protein (GFAP). Patch clamp study showed that TGF-␤ 1 (0.1-100 ng/ml) caused a rapid (<5 min) depolarization because of dose-dependent down-regulation of Kir2.3 channels, which was mimicked by the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (10 -500 nM) and which was inhibited by the PKC inhibitor calphostin C (100 nM), by PKC desensitization produced by 3 h of exposure to phorbol 12-myristate 13-acetate (100 nM), and by the PKC-␦ isoform-specific inhibitor rottlerin (50 M). Immunoblot analysis and confocal imaging showed that TGF-␤ 1 caused PKC-␦ translocation to membrane, and co-immunoprecipitation experiments showed that TGF-␤ 1 enhanced association between Kir2.3 and PKC-␦. Additional electrophysiological experiments showed that Kir2.3 channel down-regulation was blocked by the phospholipase C inhibitors, neomycin (100 M) and D609 (200 M). Given

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