Influence of rBAT-Mediated Amino Acid Transport on Cytosolic pH

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Abstract

rBAT, together with its subunit b0,+ AT mediates the hetero- and homoexchange of neutral and dibasic amino acids. Since the heteroexchange of dibasic amino acids against neutral amino acids is coupled to net transport of positive charge, this transport is electrogenic. Extracellular addition of histidine could create an inward or an outward current depending on extracellular pH (pHe) and cell membrane potential. It has been concluded that histidine may be transported in both its protonated and its neutral form. In this study measurements of cytosolic pH (pHi) were performed to test this hypothesis. As a result, addition of protonated histidine at acidic pHe to Xenopus oocytes expressing rBAT creates an inward current which is paralleled by cytosolic acidification. Both can be reduced by increase of pHe. At alkaline pHe and simultaneous depolarization of the cell membrane the effect of histidine on pHi is virtually abolished. The neutral amino acid leucine does not alter cytosolic pH at neither pH 6.0 nor at pH 8.0. In conclusion, histidine can be transported in either its neutral or its protonated form. Transport of the protonated form is facilitated by extracellular acidification and hyperpolarization of the cell membrane.

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Non-type I cystinuria caused by mutations in SLC7A9, encoding a subunit (bo,+AT) of rBAT.

Lídia Feliubadaló, Mariona Font, Jesús Purroy … (1999)

Cystinuria (MIM 220100) is a common recessive disorder of renal reabsorption of cystine and dibasic amino acids. Mutations in SLC3A1, encoding rBAT, cause cystinuria type I (ref. 1), but not other types of cystinuria (ref. 2). A gene whose mutation causes non-type I cystinuria has been mapped by linkage analysis to 19q12-13.1 (Refs 3,4). We have identified a new transcript, encoding a protein (bo, +AT, for bo,+ amino acid transporter) belonging to a family of light subunits of amino acid transporters, expressed in kidney, liver, small intestine and placenta, and localized its gene (SLC7A9) to the non-type I cystinuria 19q locus. Co-transfection of bo,+AT and rBAT brings the latter to the plasma membrane, and results in the uptake of L-arginine in COS cells. We have found SLC7A9 mutations in Libyan-Jews, North American, Italian and Spanish non-type I cystinuria patients. The Libyan Jewish patients are homozygous for a founder missense mutation (V170M) that abolishes b o,+AT amino-acid uptake activity when co-transfected with rBAT in COS cells. We identified four missense mutations (G105R, A182T, G195R and G295R) and two frameshift (520insT and 596delTG) mutations in other patients. Our data establish that mutations in SLC7A9 cause non-type I cystinuria, and suggest that bo,+AT is the light subunit of rBAT.

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Identification of an amino acid transporter associated with the cystinuria-related type II membrane glycoprotein.

H Haga, H Ito, K Miyamoto … (1999)

We identified an amino acid transporter that is associated with the cystinuria-related type II membrane glycoprotein, rBAT (related to b(0,+) amino acid transporter). The transporter designated BAT1 (b(0, +)-type amino acid transporter 1) from rat kidney was found to be structurally related to recently identified amino acid transporters for system L, system y(+)L, and system x(-)C, which are linked, via a disulfide bond, to the other type II membrane glycoprotein, 4F2hc (4F2 heavy chain). In the nonreducing condition, a 125-kDa band, which seems to correspond to the heterodimeric complex of BAT1 and rBAT, was detected in rat kidney with anti-BAT1 antibody. The band was shifted to 41 kDa in the reducing condition, confirming that BAT1 and rBAT are linked via a disulfide bond. The BAT1 and rBAT proteins were shown to be colocalized in the apical membrane of the renal proximal tubules where massive cystine transport had been proposed. When expressed in COS-7 cells with rBAT, but not with 4F2hc, BAT1 exhibited a Na(+)-independent transport of cystine as well as basic and neutral amino acids with the properties of system b(0,+). The results from the present investigation were used to establish a family of amino acid transporters associated with type II membrane glycoproteins.

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The Use of Xenopus laevis Oocytes for the Functional Characterization of Heterologously Expressed Membrane Proteins

Carsten A. Wagner, Björn Friedrich, Iwan Setiawan … (2000)

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Author and article information

Journal

Journal ID (publisher-id): NEF

Journal ID (nlm-ta): Nephron

Journal ID (doi): 10.1159/issn.1660-8151

Title: Nephron

Publisher: S. Karger AG

ISSN (Print): 1660-8151

ISSN (Electronic): 2235-3186

Publication date Subscription-year: 2002

Publication date (Print): August 2002

Publication date (Electronic): 15 July 2002

Volume: 91

Issue: 4

Pages: 631-636

Affiliations

^aDepartment of Physiology, University of Tübingen, Germany; ^bDepartment of Biochemistry, University of Barcelona, Spain

Article

Publisher ID: 65024 Other ID: Nephron 2002;91:631–636

DOI: 10.1159/000065024

PubMed ID: 12138266

SO-VID: 5ac8ba56-87a8-486c-84a4-01ca0b4733ac

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Influence of rBAT-Mediated Amino Acid Transport on Cytosolic pH

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Abstract

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Karger: Nephrology

Most cited references 6

Non-type I cystinuria caused by mutations in SLC7A9, encoding a subunit (bo,+AT) of rBAT.

Identification of an amino acid transporter associated with the cystinuria-related type II membrane glycoprotein.

The Use of Xenopus laevis Oocytes for the Functional Characterization of Heterologously Expressed Membrane Proteins

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