We discovered a new ion channel in cells from ischemic/hypoxic brain that is a potentially important novel target for therapeutic intervention in stroke. This channel is a non-selective cation channel activated by intracellular Ca2+ and blocked by intracellular ATP (NC Ca-ATP channel) that is not normally expressed in brain, but is expressed under conditions of hypoxia. When opened by depletion of intracellular ATP, this channel is responsible for complete depolarization due to massive Na+ influx, which creates an electrical gradient for Cl- and an osmotic gradient for H2O, resulting in cytotoxic edema and cell death. This channel is unusual because it is the first outside the KATP channel family that is found to be regulated by sulfonylurea receptor-1 (SUR1). Thus, cytotoxic edema and cell death normally induced by ATP depletion are prevented in vitro by the SUR1 blocker, glibenclamide. Using rodent models of permanent focal cerebral ischemia (MCAO), we found that the SUR1 regulatory subunit of this channel is up-regulated in astrocytes, neurons, and capillary endothelial cells following ischemia, and that blocking this receptor using the highly specific blocker, low-dose glibenclamide, reduces stroke size, cerebral edema and mortality, consistent with an important role for SUR1 in formation of cytotoxic and ionic edema. Using a rodent (SHR) model of thromboembolic stroke in which tPA is given 6 hr after stroke, we also obtained preliminary data that co-treatment with glibenclamide at 6 hr reduces tPA-associated hemorrhagic conversion. In this grant, we plan 4 aims to: (SA1) assess the protective effect of low dose glibenclamide in a rat model of thromboembolic stroke, including effects on tissue Na+, water, BBB disruption, hemorrhagic conversion, stroke size and neurological outcome, when tPA plus drug co-treatment are begun at various times after stroke;(SA2) assess the protective effect of SUR1 knockout (SUR1KO mice) on tissue Na+, water, BBB disruption, hemorrhagic conversion, stroke size and neurological outcome after temporary MCAO;(SA3) test the hypothesis that SUR1 upregulation in stroke is related to NCCa-ATP channel expression, and characterize channel properties in endothelial cells and neurons at neutral and at low pH;(SA4) identify transcription factors responsible for SUR1 expression in ischemia/hypoxia, including use of serial analysis of gene expression (SAGE) for assessment of tissue-specific transcription factors.
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