Renal expression of novel Na+/H+ exchanger isoform NHE8.
Although Na(+)/H(+) exchanger isoform 3 (NHE3) mediates most Na(+)/H(+) exchange in the proximal tubule, studies of NHE3/NHE2 null mice suggest residual Na(+)-dependent proton secretion (Choi JY, Shah M, Lee MG, Schultheis PJ, Shull GE, Muallem S, and Baum M. J Clin Invest 105: 1141-1146, 2000). To characterize additional NHE isoforms that might be expressed in the kidney, we identified the partial sequence of a novel NHE. PCR was used to define the 5'- and 3'-ends, and a cDNA encoding the complete open reading frame was amplified from mouse kidney. The predicted protein of 576 amino acids, which we have named NHE8, has 30-35% amino acid identity to known mammalian isoforms (NHE1-7) but has >50% identity to Drosophila melanogaster "NHE1," suggesting it is the mammalian ortholog of this ancient invertebrate isoform. Northern blot of mouse tissues revealed ubiquitous expression. Western blot using anti-NHE8 antibodies demonstrated protein expression in apical membranes purified from rat renal cortex by divalent cation precipitation. In situ hybridization revealed that NHE8 message was present in both cortex and medulla. In the cortex, NHE8 was present in the majority of cortical tubules, consistent with proximal tubule (S1 and S2) localization. In the medulla, NHE8 message was most highly expressed in the proximal tubules (S3) of the outer stripe of the outer medulla. Thus NHE8 is expressed in the proximal tubule, where it may contribute to apical membrane ion transport.
Goyal
Sunita
S
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520-8029, USA.
Vanden Heuvel
Gregory
G
Aronson
Peter S
PS
D000595:Amino Acid Sequence; D000818:Animals; D000918:Antibody Specificity; D019556:COS Cells; D027682:Cation Transport Proteins; D029721:Drosophila Proteins / Q000235:genetics; D006801:Humans; D015151:Immunoblotting; D017403:In Situ Hybridization; D007668:Kidney / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics; D051379:Mice; D008871:Microvilli / Q000378:metabolism; D008969:Molecular Sequence Data; D009928:Organ Specificity; D020033:Protein Isoforms / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000096:biosynthesis / Q000235:genetics*; D014162:Transfection
D027682:Cation Transport Proteins; D029721:Drosophila Proteins; D008565:Membrane Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; C490998:SLC9A1 protein, human; C486775:SLC9A8 protein, human; C490997:Slc9a1 protein, mouse; C471945:Slc9a8 protein, mouse; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers