title: Mechanical strain injury increases intracellular sodium and reverses Na+/Ca2+ exchange in cortical astrocytes.
abstract: Traditionally, astrocytes have been considered less susceptible to injury than neurons. Yet, we have recently shown that astrocyte death precedes neuronal death in a rat model of traumatic brain injury (TBI) (Zhao et al.: Glia 44:140-152, 2003). A main mechanism hypothesized to contribute to cellular injury and death after TBI is elevated intracellular calcium ([Ca2+]i). Since calcium regulation is also influenced by regulation of intracellular sodium ([Na+]i), we used an in vitro model of strain-induced traumatic injury and live-cell fluorescent digital imaging to investigate alterations in [Na+]i in cortical astrocytes after injury. Changes in [Na+]i, or [Ca2+]i were monitored after mechanical injury or L-glutamate exposure by ratiometric imaging of sodium-binding benzofuran isophthalate (SBFI-AM), or Fura-2-AM, respectively. Mechanical strain injury or exogenous glutamate application produced increases in [Na+]i that were dependent on the severity of injury or concentration. Injury-induced increases in [Na+]i were significantly reduced, but not completely eliminated, by inhibition of glutamate uptake by DL-threo-beta-benzyloxyaspartate (TBOA). Blockade of sodium-dependent calcium influx through the sodium-calcium exchanger with 2-[2-[4-(4-Nitrobenzyloxy)phenyl]ethyl]isothiourea mesylate (KB-R7943) reduced [Ca2+]i after injury. KB-R7943 also reduced astrocyte death after injury. These findings suggest that in astrocytes subjected to mechanical injury or glutamate excitotoxicity, increases in intracellular Na+ may be a critical component in the injury cascade and a therapeutic target for reduction of lasting deficits after traumatic brain injury.
authors.affiliation: Department of Neurological Surgery, Center for Neuroscience, University of California, Davis, California 95616-8797, USA.
authors.forename: Candace L
authors.initials: CL
authors.lastname: Floyd
authors.forename: Fredric A
authors.initials: FA
authors.lastname: Gorin
authors.forename: Bruce G
authors.initials: BG
authors.lastname: Lyeth
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000378:metabolism* / Q000473:pathology; D001693:Biological Transport, Active; D002138:Calibration; D016923:Cell Death; D002478:Cells, Cultured; D005456:Fluorescent Dyes; D018698:Glutamic Acid / Q000378:metabolism; D007424:Intracellular Fluid / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D013314:Stress, Mechanical
chemical_list: D005456:Fluorescent Dyes; D019831:Sodium-Calcium Exchanger; D018698:Glutamic Acid; D012964:Sodium