Mammalian Urea Transporters

Sands, Jeff M.

doi:10.1146/annurev.physiol.65.092101.142638

Cited by 141 publications

(103 citation statements)

References 135 publications

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“…1 A). Exon 10 codes for amino acids 291-339 of UT-A1 and is situated in a large hydrophobic region, thought to be membrane-spanning (24). Deletion of this exon and splicing from exons 9 to 11 is predicted to result in a frameshift.…”

Section: Resultsmentioning

confidence: 99%

Urinary concentrating defect in mice with selective deletion of phloretin-sensitive urea transporters in the renal collecting duct

Fenton

Chou

Stewart

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

225

230

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To investigate the role of inner medullary collecting duct (IMCD) urea transporters in the renal concentrating mechanism, we deleted 3 kb of the UT-A urea transporter gene containing a single 140-bp exon (exon 10). Deletion of this segment selectively disrupted expression of the two known IMCD isoforms of UT-A, namely UT-A1 and UT-A3, producing UT-A1͞3 ؊/؊ mice. In isolated perfused IMCDs from UT-A1͞3 ؊/؊ mice, there was a complete absence of phloretin-sensitive or vasopressin-stimulated urea transport. On a normal protein intake (20% protein diet), UT-A1͞ 3 ؊/؊ mice had significantly greater fluid consumption and urine flow and a reduced maximal urinary osmolality relative to wildtype controls. These differences in urinary concentrating capacity were nearly eliminated when urea excretion was decreased by dietary protein restriction (4% by weight), consistent with the 1958 Berliner hypothesis stating that the chief role of IMCD urea transport in the concentrating mechanism is the prevention of ureainduced osmotic diuresis. Analysis of inner medullary tissue after water restriction revealed marked depletion of urea in UT-A1͞3 ؊/؊ mice, confirming the concept that phloretin-sensitive IMCD urea transporters play a central role in medullary urea accumulation. However, there were no significant differences in mean inner medullary Na ؉ or Cl ؊ concentrations between UT-A1͞3 ؊/؊ mice and wild-type controls, indicating that the processes that concentrate NaCl were intact. Thus, these results do not corroborate the predictions of passive medullary concentrating models stating that NaCl accumulation in the inner medulla depends on rapid vasopressin-regulated urea transport across the IMCD epithelium.UT-A ͉ isolated perfused tubule ͉ vasopressin ͉ concentrating mechanism F or survival remote from water sources, terrestrial animals require effective water-conservation mechanisms. In birds and mammals, water conservation depends on specialized urinary concentrating mechanisms that reduce water excretion while maintaining solute excretion. This concentrating function is carried out in the renal medulla. In mammals, the medulla is divided into two regions, the outer medulla and the inner medulla (IM), both of which manifest increased tissue osmolality relative to the blood plasma (1). In these regions, high interstitial osmolality draws water from the renal collecting duct via aquaporin water channels, resulting in a concentrated final urine. In the outer medulla, the interstitial space is concentrated through the classic countercurrent multiplication mechanism (2) in which water and solute are separated by active NaCl transport from the water-impermeable thick ascending limb of Henle (3, 4). However, in the IM the ascending portion of Henle's loop is incapable of high rates of active transport (5, 6), implying that solute concentration in the IM occurs by a different, yet unknown mechanism.One important feature of the IM that distinguishes it from the outer medulla is its ability to accumulate large amounts of urea. Berliner ...

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Section: Resultsmentioning

confidence: 99%

Urinary concentrating defect in mice with selective deletion of phloretin-sensitive urea transporters in the renal collecting duct

Fenton

Chou

Stewart

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

225

230

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“…The two isoforms, UT-A1 and UT-A3, expressed in collecting duct show increases in urea uptake in response to agents that increase intracellular cAMP (forskolin ϩ 3-isobutyl-1-methylxanthine) when expressed in Xenopus oocytes (23). They are produced by alternative splicing from a single precursor RNA and share the same N-terminal 459 aa (24). Thus, it is impossible to assign residues phosphorylated near the N terminus (S35, S62, and S63) to either isoform.…”

Section: Discussionmentioning

confidence: 99%

Quantitative phosphoproteomics of vasopressin-sensitive renal cells: Regulation of aquaporin-2 phosphorylation at two sites

Hoffert

Pisitkun

Wang

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

325

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Protein phosphorylation plays a key role in vasopressin signaling in the renal-collecting duct. Large-scale identification and quantification of phosphorylation events triggered by vasopressin is desirable to gain a comprehensive systems-level understanding of this process. We carried out phosphoproteomic analysis of rat inner medullary collecting duct cells by using a combination of phosphopeptide enrichment by immobilized metal affinity chromatography and phosphorylation site identification by liquid chromatography-mass spectrometry n neutral loss scanning. A total of 714 phosphorylation sites on 223 unique phosphoproteins were identified from inner medullary collecting duct samples treated shortterm with either calyculin A or vasopressin. A number of proteins involved in cytoskeletal reorganization, vesicle trafficking, and transcriptional regulation were identified. Previously unidentified phosphorylation sites were found for membrane proteins essential to collecting duct physiology, including eight sites among aquaporin-2 (AQP2), aquaporin-4, and urea transporter isoforms A1 and A3. Through label-free quantification of phosphopeptides, we identified a number of proteins that significantly changed phosphorylation state in response to short-term vasopressin treatment: AQP2, Bclaf1, LRRC47, Rgl3, and SAFB2. In the presence of vasopressin, AQP2 monophosphorylated at S256 and diphosphorylated AQP2 (pS256͞261) increased in abundance, whereas AQP2 monophosphorylated at S261 decreased, raising the possibility that both sites are involved in vasopressin-dependent AQP2 trafficking. This study reveals the practicality of liquid chromotography-mass spectrometry n neutral loss scanning for large-scale identification and quantification of protein phosphorylation in the analysis of cell signaling in a native mammalian system. LC-MS͞MS ͉ collecting duct ͉ kidney ͉ Collecting Duct Phosphoprotein Database (CDPD) ͉ neutral loss E lucidation of cellular signaling networks requires methodologies for large-scale quantitative phosphoproteomic analysis that can be used to reveal dynamic system-wide changes in protein phosphorylation. Recent studies have introduced two new innovations, namely, immobilized metal affinity chromatography (IMAC) (1-3) and liquid chromatography-mass spectrometry (LC-MS) 3 neutral loss scanning (1-4), to increase the efficiency of phosphopeptide identification. Quantification of phosphopeptides in this setting has been challenging and has been successful so far in cultured cells (5) and yeast (6) but not in native mammalian cells and tissues. Here, we introduce a hybrid approach using IMAC for phosphopeptide enrichment, LC-MS multisequential (LC-MS n ) neutral loss scanning to identify phosphorylated residues in the peptides, and label-free quantification using numerical integration of pseudochromatograms constructed from MS peak heights.The method is used here for analysis of protein phosphorylation in vasopressin-sensitive inner medullary collecting duct (IMCD) cells freshly isolated from rat kidneys. ...

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“…Therefore, it appears that the urea-N permeability Table 2 Mean arterial urea-N concentrations (MAUN), minimum and maximum treatment means for net portal-drained viscera (PDV) uptake of arterial urea-N relative to N intake (%, PDVU), and minimum and maximum sum of ammonia and urea-N fluxes across the PDV relative to N intake (%, PDVAU Table 1. of the epithelia lining the gut, including the rumen epithelium, is regulated, and gut epithelial permeability for urea is most likely increased when cattle are fed low N diets. The identification of urea-N transport proteins (Sands, 2003) has provided support to the hypothesis that it is the urea-N permeability of the epithelial membranes that is regulated by the cow and the existence of transporters has also provided a framework for thinking of urea-N fluxes as something regulated by concentration or activity of integral membrane proteins. However, despite convincing evidence of urea transporter B (UT-B) expression in stratum basale, spinosum and granulosum of the rumen epithelium (Graham and Simmons, 2004;Stewart et al, 2005), it has not been possible to demonstrate a correlation between reduced dietary N intake and upregulation of UT-B expression in sheep or cattle (Marini and Van Amburgh, 2003;Marini et al, 2004).…”

Section: Impact Of N Recycling On the Efficiency Of N Utilization In mentioning

confidence: 95%

“…Streptococcus bovis, Ruminoccocus amylophylus and Prevotella spp), making it more suitable for control (Walker et al, 2005). Wallace et al (2001 and2003) provided some evidence that the modification of the Prevotella ssp. population or the direct inhibition of the enzyme dipeptidyl peptidase involved in Nitrogen utilization in ruminants oligopeptide degradation may help in reducing the degradation rate of oligopeptides.…”

Section: Microbial Protein Synthesismentioning

confidence: 99%

Strategies for optimizing nitrogen use by ruminants

Calsamiglia

Ferret

Reynolds

et al. 2010

Animal

251

165

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The efficiency of N utilization in ruminants is typically low (around 25%) and highly variable (10% to 40%) compared with the higher efficiency of other production animals. The low efficiency has implications for the production performance and environment. Many efforts have been devoted to improving the efficiency of N utilization in ruminants, and while major improvements in our understanding of N requirements and metabolism have been achieved, the overall efficiency remains low. In general, maximal efficiency of N utilization will only occur at the expense of some losses in production performance. However, optimal production and N utilization may be achieved through the understanding of the key mechanisms involved in the control of N metabolism. Key factors in the rumen include the efficiency of N capture in the rumen (grams of bacterial N per grams of rumen available N) and the modification of protein degradation. Traditionally, protein degradation has been modulated by modifying the feed (physical and chemical treatments). Modifying the rumen microflora involved in peptide degradation and amino acid deamination offers an alternative approach that needs to be addressed. Current evidence indicates that in typical feeding conditions there is limited net recycling of N into the rumen (blood urea-N uptake minus ammonia-N absorption), but understanding the factors controlling urea transport across the rumen wall may reverse the balance to take advantage of the recycling capabilities of ruminants. Finally, there is considerable metabolism of amino acids (AA) in the portal-drained viscera (PDV) and liver. However, most of this process occurs through the uptake of AA from the arterial blood and not during the 'absorptive' process. Therefore, AA are available to the peripheral circulation and to the mammary gland before being used by PDV and the liver. In these conditions, the mammary gland plays a key role in determining the efficiency of N utilization because the PDV and liver will use AA in excess of those required by the mammary gland. Protein synthesis in the mammary gland appears to be tightly regulated by local and systemic signals. The understanding of factors regulating AA supply and absorption in the mammary gland, and the synthesis of milk protein should allow the formulation of diets that increase total AA uptake by the mammary gland and thus reduce AA utilization by PDV and the liver. A better understanding of these key processes should allow the development of strategies to improve the efficiency of N utilization in ruminants. Keywords: ruminant, nitrogen efficiency ImplicationsRuminants have a low efficiency of N utilization compared with non-ruminants. This low efficiency has implications not only for production performance and economic efficiency but also for the emission of contaminants to the environment. The efficiency of N utilization can be improved through the understanding and modification of factors regulating the efficiency of N utilization in key processes, including N capture in the rumen, ...

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Mammalian Urea Transporters

Cited by 141 publications

References 135 publications

Urinary concentrating defect in mice with selective deletion of phloretin-sensitive urea transporters in the renal collecting duct

Urinary concentrating defect in mice with selective deletion of phloretin-sensitive urea transporters in the renal collecting duct

Quantitative phosphoproteomics of vasopressin-sensitive renal cells: Regulation of aquaporin-2 phosphorylation at two sites

Strategies for optimizing nitrogen use by ruminants

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