A major task of the kidney tubule is to reabsorb filtered HCO-3 and generate """"""""new"""""""" HCO-3, thereby preventing a fatal metabolic acidosis. About 80 percent of HCO-3 reabsorption and generation occurs in the proximal tubule (PT), which secretes H+ into the tubule lumen, titrating HCO-3 to CO2 + H2O. After entering the PT cell, the CO2 + H2O regenerate HCO-3, which exits across the basolateral membrane via the electrogenic Na/HCO3 cotransporter (NBCe1-A). Since the Pl's laboratory reported the expression cloning of this cotransporter nearly 5 yrs ago, both """"""""pancreatic"""""""" (NBCe1-B) and """"""""brain"""""""" (NBCe1-C) splice variants have been identified. These cotransporters play key roles in HCO-3 transport by other epithelia, and in pHi regulation by many cell types. NBCe1 is part of the Bicarbonate Transporter (BT) superfamily, along with the C1-HCO3 exchangers (AEs), two other Na+ -coupled HCO-3 transporters (the electroneutral NBC and the Na+ -driven C1-HCO3 exchanger), related proteins not yet fully characterized, and at least one new gene (known from human genome sequence). The major goal of this project is to elucidate the molecular physiology of electrogenic NBCs, particularly in the kidney. An ancillary goal is to elucidate the expression of other Na+ -coupled HCO-3 transporters in key renal cell types. The proposed work has three aims: (i) Develop molecular tools. We will obtain the cDNA for a new NBCe-related sequence identified in the genome, extend our panel of type-specific antibodies, and determine the localization of Na+ -coupled HCO-3 transporters in the kidney. (ii) Determine properties of wild- type electrogenic NBCs. Using heterologous expression in oocytes, we will determine the function of two cDNA clones likely to encode electrogenic NBCs. We will also determine the stoichiometry of the electro-genic NBCs; assess their dependence on Na+, HCO-3 and pH; ask whether they transport CO=3; characterize the interaction between NBCe1 and carbonic anhydrase II; and examine the action of PKA on NBCe1 in oocytes. (iii) Analyze structure-function relationships. We will determine the structural requirements for extra- and intracellular DIDS sensitivity, ask whether conserved putative DIDS-reaction motifs are involved in electrostatic trapping of HCO-3, assess naturally occurring human NBCe1 mutations, explore the topology of NBCe1, and-in collaboration with another laboratory-study the biochemistry of the isolated cytoplasmic N termini of NBCe1-A and -B. The proposed work should elucidate the role that the electrogenic Na/HCO3 cotransporter plays in renal function, both in health and disease. The results could have important implications for understanding the normal control of acid-base balance and renal-tubule acidosis.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Method to Extend Research in Time (MERIT) Award (R37)
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General Medicine B Study Section (GMB)
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Ketchum, Christian J
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Yale University
Schools of Medicine
New Haven
United States
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Jalali, R; Guo, J; Zandieh-Doulabi, B et al. (2014) NBCe1 (SLC4A4) a potential pH regulator in enamel organ cells during enamel development in the mouse. Cell Tissue Res 358:433-42
Lee, Seong-Ki; Boron, Walter F; Parker, Mark D (2013) Substrate specificity of the electrogenic sodium/bicarbonate cotransporter NBCe1-A (SLC4A4, variant A) from humans and rabbits. Am J Physiol Renal Physiol 304:F883-99
Lee, Seong-Ki; Boron, Walter F; Parker, Mark D (2013) Monitoring ion activities in and around cells using ion-selective liquid-membrane microelectrodes. Sensors (Basel) 13:984-1003
Parker, Mark D; Boron, Walter F (2013) The divergence, actions, roles, and relatives of sodium-coupled bicarbonate transporters. Physiol Rev 93:803-959
Romero, Michael F; Chen, An-Ping; Parker, Mark D et al. (2013) The SLC4 family of bicarbonate (HCOýýýýýý) transporters. Mol Aspects Med 34:159-82
Gill, Harindarpal S; Dutcher, Lauren; Boron, Walter F et al. (2013) X-ray diffraction studies on merohedrally twinned ?1-62NtNBCe1-A crystals of the sodium/bicarbonate cotransporter. Acta Crystallogr Sect F Struct Biol Cryst Commun 69:796-9
Hill, Jacqueline; Lee, Seong-Ki; Samasilp, Prattana et al. (2012) Pituitary adenylate cyclase-activating peptide enhances electrical coupling in the mouse adrenal medulla. Am J Physiol Cell Physiol 303:C257-66
Chen, Li-Ming; Qin, Xue; Moss, Fraser J et al. (2012) Effect of simultaneously replacing putative TM6 and TM12 of human NBCe1-A with those from NBCn1 on surface abundance in Xenopus oocytes. J Membr Biol 245:131-40
Parker, Mark D; Qin, Xue; Williamson, Rosalind C et al. (2012) HCO(3)(-)-independent conductance with a mutant Na(+)/HCO(3)(-) cotransporter (SLC4A4) in a case of proximal renal tubular acidosis with hypokalaemic paralysis. J Physiol 590:2009-34
Somersalo, Erkki; Occhipinti, Rossana; Boron, Walter F et al. (2012) A reaction-diffusion model of CO2 influx into an oocyte. J Theor Biol 309:185-203

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