Genomes and Genes
Na/Bicarbonate Cotransporters in Brain
Principal Investigator: MARK BEVENSEE
Abstract: Many acid-base transporters contribute to inll'acellular and extracellular pH regul ation in brain. Electroge nic Na/Bicarbonatc Cotransp0l1crs (NBes) arc particu larly imp0l1ant because they al ter pH in response to neuronal activity. While the physiologic significance of multiple NBC vnriants in brain and other tissues is not known, many of these variants exhibit different regulatory profiles. NBCs are regulated by classic second messengers involving protein kinases A and C, as well as interacting proteins. However, the role of other regulatory pathways involving phospholipids for instance has 110t been elucida ted. '111e longterm objective of this proposal is to identify and characterize the regulatory mechanisms of Na+-coupled bit:arbonatt! transporters (BTs) in an effort to understand the significance of multiple 13Ts nnd the Illo leculnl'u'lsis of tramipo rler function. Patch-clamp techniques and fluo rcsccnce imaging will he used to exam inc phosphatidylinositol 4,S- hisphosphnte (PIP:!) regulation of pHi and ncid extrudcrs (e.g., NBCs, the Nadrivcn CI-HCO,j exchanger (NDCD E), and )./a-H exchangers (NHEs)) in cult ured astroc)'tes and neurons from rat hippocampus (Aim I). Int racellular P I P ~ levels will be altered in cells by di rect perfusion. b~lth incubation with cell ~ p e r m cant PI P", and transfection with phosphoinositide enzymes. Changes in cell ular PIP" will be <lsst!ssed by mass spectroscopy and a protein~ l ipid overlay assay. Characteristics to be examined include PJ P~ ECso, Na~ and voltuge dependencies, and sensitivity to charge scrccners and PIP2 blocJ.;ing nn tibodies. According to preliminary data, PIP" stimulates the activity of NBCe l va riants by modulating the rcgulatOlY role of thei r cytoplasmic amino termini (Aim 2). In Aim 2 , two-eleetrode voltage-damp and macropatch techniques with Xenopus ooC)"tes heterologously expressing trunca ted "mel mutant i\BCt'l va riants will be uscd to identify and characterize N terminal regions/ residues th at modulate transporter fUllction and PIP:: sensiti\ity. PIP ~ dose-response eurves will be generated. The effect of PIP:! on the biophysical properties (e .g., KM val lies for tl'ansported ions, Vlll~.~ va lu~ s, and current-voltage relationships) of NBCCl variants will be assessed. The effect of peptides containing id enti fied rcglliatory regions on NBC fU ll ction will be 'lssessed. The results from these aims will elucidate PIP~ as a novel regulatory mechanism of NBC activi ty that likely provi des a permissi\'c pH environment for PIP2 targets that modulate neuronal t'xcitahility. Characterizing the molecular basis of P[P2's sti mulation of NBCel extends our lmderstanding of tht! importance of multiple NBCs, and provides mechanistic and st ructural insight in to ~mc function. The information \,;;1\ enhance our understa nding of acid -base handling by brain cells, partieul arly in acid-base disturbances associ:Jted \,;;th ischemia, anoxia/ hypoxia, stroh, and reperftlsion inj ury.
Funding Period: ----------------2003 - ---------------2011-
more information: NIH RePORT
- Electrogenic Na/HCO3 cotransporter (NBCe1) variants expressed in Xenopus oocytes: functional comparison and roles of the amino and carboxy terminiSuzanne D McAlear
Department of Physiology and Biophysics, University of Alabama at Birmingham, 35294, USA
J Gen Physiol 127:639-58. 2006..Removing the entire cytosolic carboxy terminus of NBCe1-C, or the different carboxy terminus of the A/B variants, causes a loss of NBC activity due to low expression at the plasma membrane...
- A cysteine-scanning mutagenesis study of transmembrane domain 8 of the electrogenic sodium/bicarbonate cotransporter NBCe1Suzanne D McAlear
Department of Physiology and Biophysics, University of Alabama at Birmingham, 1918 University Boulevard, Birmingham, AL 35294, USA
J Biol Chem 281:32417-27. 2006..In summary, TMD8 residues of NBCe1, particularly L750, are involved in ion translocation, and accessibility is influenced by the state of transporter activity...
- Inhibition of the Na/bicarbonate cotransporter NBCe1-A by diBAC oxonol dyes relative to niflumic acid and a stilbeneXiaofen Liu
Department of Physiology and Biophysics, University of Alabama at Birmingham, 831 MCLM, 1918 University Boulevard, Birmingham, AL 35294 0005, USA
J Membr Biol 215:195-204. 2007..Therefore, the diBAC dyes compete with DIDS but not appreciably with Na(+) or HCO(3)(-) for binding. The mechanism of diBAC inhibition of NBCe1 appears similar to that previously reported for AE1...
- Effects of acute hypoxia on intracellular-pH regulation in astrocytes cultured from rat hippocampusMark O Bevensee
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06520, USA
Brain Res 1193:143-52. 2008....
- Localization of electrogenic Na/bicarbonate cotransporter NBCe1 variants in rat brainD Majumdar
Department of Physiology and Biophysics, University of Alabama at Birmingham, 1918 University Boulevard, 812 MCLM, Birmingham, AL 35294, USA
Neuroscience 155:818-32. 2008..In summary, the B and C variants are the predominant NBCe1 variants in rat brain and exhibit different localization profiles...
- PIP2 hydrolysis stimulates the electrogenic Na+-bicarbonate cotransporter NBCe1-B and -C variants expressed in Xenopus laevis oocytesIan M Thornell
Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, 1918 University Blvd, Birmingham, AL 35294 0005, USA
J Physiol 590:5993-6011. 2012....
- Phosphatidylinositol 4,5-bisphosphate (PIP2) stimulates the electrogenic Na/HCO3 cotransporter NBCe1-A expressed in Xenopus oocytesJianping Wu
Department of Physiology and Biophysics, Nephrology Research and Training Center, Center of Glial Biology in Medicine, University of Alabama at Birmingham, Birmingham, AL 35294, USA
Proc Natl Acad Sci U S A 106:14150-5. 2009..Spermine, poly-D-lysine, and neomycin all reduced the baseline HCO(3)(-)-induced inward currents by as much as 85%. In summary, PIP(2) stimulates NBCe1-A activity, and phosphoinositides are regulators of bicarbonate transporters...
- Sodium-bicarbonate cotransporter NBCn1 in the kidney medullary thick ascending limb cell line is upregulated under acidic conditions and enhances ammonium transportSoojung Lee
Department of Physiology, Emory University School of Medicine, Atlanta, GA 30322, USA
Exp Physiol 95:926-37. 2010..We propose that, in acidic conditions, DIDS-sensitive HCO(3)(-) extrusion is inactivated, while NBCn1 is upregulated to stimulate NH(4)(+) transport...
- Na-coupled bicarbonate transporters of the solute carrier 4 family in the nervous system: function, localization, and relevance to neurologic functionD Majumdar
Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, AL 35294, USA
Neuroscience 171:951-72. 2010..Thus, recent studies expand our understanding of the role of NCBTs in regulating the pH and ionic composition of the nervous system that can modulate neuronal activity...