The Renal Clearance of Amino Acids in Cystinuria*

Crawhall, J. C.; Scowen, E. F.; Thompson, C. J.; Watts, R. W. E.

doi:10.1172/jci105609

Cited by 66 publications

(14 citation statements)

References 21 publications

(24 reference statements)

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“…Because Ͼ90% of cystine reabsorption occurs in early parts of the proximal tubule (49,53), the rBAT-b 0,ϩ AT heterodimer is the main apical cystine reabsorption system in the kidney. This conclusion is also consistent with the finding that cystinuria patients have clearance ratios of cystine/inulin (or creatinine) of ϳ1 or even slightly higher, and they reabsorb very little cystine (only occasionally Ͼ25%) (11,17).…”

Section: Discussionsupporting

confidence: 90%

rBAT-b^0,+AT heterodimer is the main apical reabsorption system for cystine in the kidney

Fernández

Carrascal

Rousaud

et al. 2002

American Journal of Physiology-Renal Physiology

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Ferná ndez, Esperanza, Montserrat Carrascal, Ferran Rousaud, Joaquín Abiá n, Antonio Zorzano, Manuel Palacín, and Josep Chillaró n. rBAT-b 0,ϩ AT heterodimer is the main apical reabsorption system for cystine in the kidney. Am J Physiol Renal Physiol 283: F540-F548, 2002. First published March 19, 2002 10.1152/ajprenal. 00071.2002Mutations in the rBAT and b 0,ϩ AT genes cause type I and non-type I cystinuria, respectively. The disulfide-linked rBAT-b 0,ϩ AT heterodimer mediates high-affinity transport of cystine and dibasic amino acids (b 0,ϩ -like activity) in heterologous cell systems. However, the significance of this heterodimer for cystine reabsorption is unknown, as direct evidence for such a complex in vivo is lacking and the expression patterns of rBAT and b 0,ϩ AT along the proximal tubule are opposite. We addressed this issue by biochemical means. Western blot analysis of mouse and human kidney brush-border membranes showed that rBAT and b 0,ϩ AT were solely expressed as heterodimers of identical size and that both proteins coprecipitated. Moreover, quantitative immunopurification of b 0,ϩ AT followed by SDS-PAGE and mass spectrometry analysis established that b 0,ϩ AT heterodimerizes exclusively with rBAT. Together with cystine reabsorption data, our results demonstrate that a decreasing expression gradient of heterodimeric rBATb 0,ϩ AT along the proximal tubule is responsible for virtually all apical cystine reabsorption. As a corollary of the above, there should be an excess of rBAT expression over that of b 0,ϩ AT protein in the kidney. Indeed, complete immunodepletion of b 0,ϩ AT did not coprecipitate Ͼ20-30% of rBAT. Therefore, another rBAT-associated subunit may be present in latter parts of the proximal tubule. proximal tubule; heterodimeric amino acid transporter; expression gradient CLASSIC CYSTINURIA IS DUE to the impaired renal reabsorption of cystine and dibasic amino acids. Low cystine solubility causes the deposition of cystine calculi, which eventually leads to kidney failure (34). Reabsorption of cystine has been the object of a great research effort (32, 39). Dent and Rose (12) proposed a defective apical cystine transporter shared with dibasic amino acids as the main cause for cystinuria. Evidence for this hypothesis came recently with the identification of the two cystinuria genes: SLC3A1, which codes for the rBAT protein and is responsible for type I cystinuria, and SLC7A9, which codes for b 0,ϩ AT and causes non-type I cystinuria (5,14,40). Together, mutations in these two genes account for ϳ80% of cystinuria patients (16,33). b 0,ϩ AT and rBAT belong to the family of heteromeric amino acid transporters (HAT), which are made up of two structurally different subunits (10,51,54). The heavy subunit is a type II membrane glycoprotein, whereas the light subunit is an unglycosylated membrane protein bearing 12 putative transmembrane domains. Two conserved cysteines form a disulfide-linked heterodimer between the two subunits (37). A trafficking role has been proposed for the heavy sub...

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Section: Discussionsupporting

confidence: 90%

rBAT-b^0,+AT heterodimer is the main apical reabsorption system for cystine in the kidney

Fernández

Carrascal

Rousaud

et al. 2002

American Journal of Physiology-Renal Physiology

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“…A small precession peak of L-cystine was noted in some animals (Fig. 6), suggesting a slight "secretion" at the distal sites, as previously noted (14)(15)(16)(17) . In nor-kidneys was identical in normal rats.…”

Section: Introductionsupporting

confidence: 74%

Membrane permeability as a cause of transport defects in experimental Fanconi syndrome. A new hypothesis.

Bergeron¹,

Dubord²,

Hausser³

et al. 1976

J. Clin. Invest.

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A B S T R A C T The injection of sodium maleate (200-400 mg/kg) into rats produces aminoaciduria along with glycosuria and phosphaturia, resembling the Fanconi syndrome. This experimental model was studied by means of microinjections into proximal convoluted tubules of the kidney, stop-flow diuresis, and microperfusion of single nephrons. Our results show that, in maleate-treated rats, competition between amino acids of related structures (L-proline, L-OH-proline, and glycine) possesses the same characteristics, and net influx of amino acids appear normal at the proximal nephron. Data obtained by classical stop-flow techniques and single nephron microperfusions also indicate a normal entry of labeled amino acids (L-lysine, glycine, L-valine, L-proline, L-cystine), and 3-0-methyl-D-[3H]glucose and ['P]phosphate from the luminal side of the proximal tubule cell. However, the efflux of molecules from the cell appears enhanced throughout the proximal and distal tubule; molecules that exit at this site are excreted directly into the urine. Our results suggest that the phosphaturia, aminoaciduria, and glycosuria of the experimental Fanconi syndrome can be explained by a modification of the cell membrane permeability (increased efflux) at distal sites of the nephron rather than by a modification of the membrane transport (decreased influx) at the proximal sites, as is currently accepted. Our data also stress the importance of efflux phenomena in membrane transport.

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“…This was also observed by others (25,33). In our patients, tubular secretion of cystine does not appear to be restricted to either of the two genetic types, since we encountered it in both types of homozygotes.…”

Section: Intestinal Handling Of Amino Acidssupporting

confidence: 90%

Biochemical and genetic studies in cystinuria: observations on double heterozygotes of genotype I/II

Morin¹,

Thompson²,

Jackson³

et al. 1971

J. Clin. Invest.

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A B S T R A C T 10 families with cystinuria were investigated by measuring: (a) quantitative 24 hr urinary excretion of amino acids by column chromatography; (b) endogenous renal clearances of amino acids and creatinine; (c) intestinal uptake of 1'C-labeled L-cystine, L-lysine, and L-arginine using jejunal mucosal biopsies; (d) oral cystine loading tests. All four of these were studied in the probands and the first two in a large number of the family members.49 members of 8 families were found to have a regular genetic pattern as described previously by Harris, Rosenberg, and their coworkers.Clinical or biochemical differences between the homozygotes type I (recessive cystinuria) and homozygotes type II (incompletely recessive cystinuria) have not been found. Both types excreted similarly excessive amounts of cystine, lysine, arginine, and ornithine, and had high endogenous renal clearances for these four amino acids. Some homozygotes of both types had a cystine clearance higher than the glomerular filtration rate. Jejunal mucosa from both types of homozygotes exhibited near complete inability to concentrate cystine and lysine in vitro. This was also documented in vivo with oral cystine loads.The heterozygotes type I were phenotypically normal with respect to the above four measurements. The heterozygotes typ)e II showed moderate but definite abnormalities in their urinary excretion and their renal Dr. Morin is recipient of a medical research council fellowship. This work forms part of a

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The Renal Clearance of Amino Acids in Cystinuria*

Cited by 66 publications

References 21 publications

rBAT-b^0,+AT heterodimer is the main apical reabsorption system for cystine in the kidney

rBAT-b^0,+AT heterodimer is the main apical reabsorption system for cystine in the kidney

Membrane permeability as a cause of transport defects in experimental Fanconi syndrome. A new hypothesis.

Biochemical and genetic studies in cystinuria: observations on double heterozygotes of genotype I/II

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The Renal Clearance of Amino Acids in Cystinuria*

Cited by 66 publications

References 21 publications

rBAT-b0,+AT heterodimer is the main apical reabsorption system for cystine in the kidney

rBAT-b0,+AT heterodimer is the main apical reabsorption system for cystine in the kidney

Membrane permeability as a cause of transport defects in experimental Fanconi syndrome. A new hypothesis.

Biochemical and genetic studies in cystinuria: observations on double heterozygotes of genotype I/II

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rBAT-b^0,+AT heterodimer is the main apical reabsorption system for cystine in the kidney

rBAT-b^0,+AT heterodimer is the main apical reabsorption system for cystine in the kidney