Critical role of sodium in cytosolic [Ca2+] elevations in cultured hippocampal CA1 neurons during anoxic depolarization.
Although the extent of ischemic brain damage is directly proportional to the duration of anoxic depolarization (AD), the mechanism of cytosolic [Ca(2+)] ([Ca(2+)](c)) elevation during AD is poorly understood. To address the mechanism in this study, [Ca(2+)](c) was monitored in cultured rat hippocampal CA1 neurons loaded with a Ca-sensitive dye, fura-2FF, and exposed to an AD-simulating medium containing (in mmol/L): K(+) 65, Na(+) 50, Ca(2+) 0.13, glutamate 0.1, and pH reduced to 6.6. Application of this medium promptly elevated [Ca(2+)](c) to about 30 micromol/L, but only if oxygen was removed, the respiratory chain was inhibited, or if the mitochondria were uncoupled. These high [Ca(2+)](c) elevations depended on external Ca(2+) and could not be prevented by inhibiting NMDA or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainate receptors, or gadolinium-sensitive channels. However, they could be prevented by removing external Na(+) or simultaneously inhibiting NMDA and AMPA/kainate receptors; 2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea methanesulfonate (KB-R7943), an inhibitor of plasmalemmal Na(+)/Ca(2+) exchanger, partly suppressed them. The data indicate that the [Ca(2+)](c) elevations to 30 micromol/L during AD result from Na(+) influx. Activation of either NMDA or AMPA/kainate channels provides adequate Na(+) influx to induce these [Ca(2+)](c) elevations, which are mediated by KB-R7943-sensitive and KB-R7943-resistant mechanisms.
Kiedrowski
Lech
L
The Psychiatric Institute, Departments of Psychiatry and Pharmacology, The University of Illinois at Chicago, Chicago, IL 60612, USA. lkiedr@psych.uic.edu
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D004347:Drug Interactions; D004622:Embryo, Mammalian; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005260:Female; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D018698:Glutamic Acid / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology*; D000860:Hypoxia / Q000473:pathology / Q000503:physiopathology*; D007150:Immunohistochemistry / Q000379:methods; D009474:Neurons / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D011247:Pregnancy; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D014404:Tubulin / Q000378:metabolism
D004791:Enzyme Inhibitors; D018691:Excitatory Amino Acid Antagonists; D005904:Glial Fibrillary Acidic Protein; D014404:Tubulin; D018698:Glutamic Acid; D012964:Sodium; D002118:Calcium