Sodium/bicarbonate cotransporter NBCn1/slc4a7 increases cytotoxicity in magnesium depletion in primary cultures of hippocampal neurons

• Type of Material: Article
• Authors: Deborah S. Cooper, Emory University; Han Soo Yang, Emory University; Peijian He, Emory University; Eunjin Kim, Emory University; Ira Rajbhandari, Emory University; Chris Yun, Emory University; Inyeong Choi, Emory University
• Language: English
• Date: 2009-02
• Publisher: Wiley: 12 months
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © The Authors (2008). Journal Compilation © Federation of European Neuroscience Societies and Blackwell Publishing Ltd
• Final Published Version (URL): http://onlinelibrary.wiley.com/doi/10.1111/j.1460-9568.2008.06611.x/abstract
• Title of Journal or Parent Work: European Journal of Neuroscience
• ISSN: 0953-816X
• Volume: 29
• Issue: 3
• Start Page: 437
• End Page: 446
• Grant/Funding Information: This work was supported by the American Heart Association Southeast Affiliate and the URC grant at Emory (I.C.), and NIH DK61418 (C.C.Y).
• Keywords: pH; Na/HCO3 transporter; ischemia; SLC4A7; acid
• Research Categories: Biology, Physiology; Health Sciences, Pharmacology

Abstract

Growing evidence suggests that pharmacological inhibition of Na/H exchange and Na/HCO3 transport provides protection against damage or injury in cardiac ischemia. In this study, we examined the contribution of the sodium/bicarbonate cotransporter NBCn1 (slc4a7) to cytotoxicity in cultured hippocampal neurons of rats. In neurons exposed to extracellular pH (pHo) ranging from 6.2 to 8.3, NBCn1 protein expression increased by fivefold at pH < 6.5 compared to the expression at pHo 7.4. At pHo 6.5, the intracellular pH of neurons was ~1 unit lower than that at pH 7.4. Immunochemistry showed a marked increase in NBCn1 immunofluorescence in plasma membranes and cytosol of the soma as well as in dendrites, at pHo 6.5. NBCn1 expression also increased by 40% in a prolonged Mg2+-free incubation at normal pHo. Knockdown of NBCn1 in neurons had negligible effect on cell viability. The effect of NBCn1 knockdown on cytotoxicity was then determined by exposing neurons to 0.5 mM glutamate for 10 min and measuring lactate dehydrogenase (LDH) release from neurons. Compared to normal incubation (pHo 7.2 for 6 h) after glutamate exposure, acidic incubation (pHo 6.3 for 6 h) reduced cytotoxicity by 75% for control neurons and 78% for NBCn1-knockdown neurons. Thus, both controls and knockdown neurons showed acidic protection from cytotoxicity. However, in Mg2+-free incubation after glutamate exposure, NBCn1 knockdown progressively attenuated cytotoxicity. This attenuation was unaffected by acidic preincubation before glutamate exposure. We conclude that NBCn1 has a dynamic upregulation in low pHo and Mg2+ depletion. NBCn1 is not required for acidic protection, but increases cytotoxicity in Mg2+-free conditions.