In depolarized and glucose‐deprived neurons, Na+ influx reverses plasmalemmal K+‐dependent and K+‐independent Na+/Ca2+ exchangers and contributes to NMDA excitotoxicity

• Published in: Journal of neurochemistry 2002-12, Vol.83 (6), p.1321-1328
• Main Authors: Czyż, Aneta, Kiedrowski, Lech
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - metabolism; Animals; ATP depletion; Biochemistry and metabolism; Biological and medical sciences; Calcium - metabolism; Calcium Radioisotopes; Cell Membrane Structures - metabolism; Cell Survival - drug effects; Cells, Cultured; Central nervous system; Cesium - pharmacology; Fundamental and applied biological sciences. Psychology; Glucose - deficiency; Glucose - metabolism; glucose deprivation; gramicidin; Gramicidin - pharmacology; ischemia; KB‐R7943; Lithium - pharmacology; N-Methylaspartate - toxicity; Neurons - cytology; Neurons - drug effects; Neurons - metabolism; Potassium - metabolism; Rats; Rats, Sprague-Dawley; Sodium - metabolism; Sodium-Calcium Exchanger - antagonists & inhibitors; Sodium-Calcium Exchanger - metabolism; Sodium-Potassium-Exchanging ATPase - antagonists & inhibitors; sodium–calcium exchange; Thiourea - analogs & derivatives; Thiourea - pharmacology; Vertebrates: nervous system and sense organs
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1046/j.1471-4159.2002.01227.x

Cerebellar granule cells (CGCs) express K+‐dependent (NCKX) and K+‐independent (NCX) plasmalemmal Na+/Ca2+ exchangers which, under plasma membrane‐depolarizing conditions and high cytosolic [Na+], may reverse and mediate potentially toxic Ca2+ influx. To examine this possibility, we inhibited NCX or NCKX with KB‐R7943 or K+‐free medium, respectively, and studied how gramicidin affects cytosolic [Ca2+] and 45Ca2+ accumulation. Gramicidin forms pores permeable to alkali cations but not Ca2+. Therefore, gramicidin‐induced Ca2+ influx is indirect; it results from fluxes of monovalent cations. In the presence of Na+, but not Li+ or Cs+, gramicidin induced Ca2+ influx that was inhibited by simultaneous application of KB‐R7943 and K+‐free medium. The data indicate that gramicidin‐induced Na+ influx reverses NCX and NCKX. To test the role of NCX and/or NCKX in excitotoxicity, we studied how NMDA affects the viability of glucose‐deprived and depolarized CGCs. To assure depolarization of the plasma membrane, we inhibited Na+,K+‐ATPase with ouabain. Although inhibition of NCX or NCKX reversal failed to significantly limit 45Ca2+ accumulation and excitotoxicity, simultaneously inhibiting NCX and NCKX reversal was neuroprotective and significantly decreased NMDA‐induced 45Ca2+ accumulation. Our data suggest that NMDA‐induced Na+ influx reverses NCX and NCKX and leads to the death of depolarized and glucose‐deprived neurons.