Bumetanide inhibition of the blood-brain barrier Na-K-Cl cotransporter reduces edema formation in the rat middle cerebral artery occlusion model of stroke.
Increased transport of Na+ across an intact blood-brain barrier (BBB) participates in edema formation during the early hours of cerebral ischemia. In previous studies, the authors showed that the BBB Na-K-Cl cotransporter is stimulated by factors present during ischemia, suggesting that the cotransporter may contribute to the increased brain Na+ uptake in edema. The present study was conducted to determine (1) whether the Na-K-Cl cotransporter is located in the luminal membrane of the BBB, and (2) whether inhibition of the BBB cotransporter reduces brain edema formation. Perfusion-fixed rat brains were examined for cotransporter distribution by immunoelectron microscopy. Cerebral edema was evaluated in rats subjected to permanent middle cerebral artery occlusion (MCAO) by magnetic resonance diffusion-weighted imaging and calculation of apparent diffusion coefficients (ADC). The immunoelectron microscopy studies revealed a predominant (80%) luminal membrane distribution of the cotransporter. Magnetic resonance imaging studies showed ADC ratios (ipsilateral MCAO/contralateral control) ranging from 0.577 to 0.637 in cortex and striatum, indicating substantial edema formation. Intravenous bumetanide (7.6-30.4 mg/kg) given immediately before occlusion attenuated the decrease in ADC ratios for both cortex and striatum (by 40-67%), indicating reduced edema formation. Bumetanide also reduced infarct size, determined by TTC staining. These findings suggest that a luminal BBB Na-K-Cl cotransporter contributes to edema formation during cerebral ischemia.
O'Donnell
Martha E
ME
Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis 95616, USA. meodonnell@ucdavis.edu
Tran
Lien
L
Lam
Tina I
TI
Liu
Xiao Bo
XB
Anderson
Steven E
SE
D000818:Animals; D001812:Blood-Brain Barrier / Q000187:drug effects / Q000378:metabolism*; D001929:Brain Edema / Q000188:drug therapy / Q000209:etiology / Q000378:metabolism*; D002034:Bumetanide / Q000494:pharmacology*; D038524:Diffusion Magnetic Resonance Imaging; D004232:Diuretics / Q000494:pharmacology*; D020244:Infarction, Middle Cerebral Artery / Q000150:complications / Q000188:drug therapy / Q000378:metabolism*; D016253:Microscopy, Immunoelectron; D051381:Rats; D017207:Rats, Sprague-Dawley; D028021:Sodium-Potassium-Chloride Symporters / Q000187:drug effects / Q000378:metabolism*
D004232:Diuretics; D028021:Sodium-Potassium-Chloride Symporters; D002034:Bumetanide