Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P41181 (collecting duct)
 5,183 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A significant percentage of excreted ammonium is added to tubular fluid along the medullary collecting duct. However, it is not clear whether this ammonia is produced in the cortex and delivered into the medulla or is produced directly by medullary cells. To address this issue, rat epithelial cells derived from the renal papilla were grown in continuous culture and their ability to generate ammonia was examined. When grown in Dulbecco's modified Eagle's medium with 4 mM glutamine, these cells produced ammonia at a rate of approximately 27 nmol/10(6) cells/h. When these cells were grown in minimum essential medium without glutamine, ammonia production fell to 7 nmol/10(6) cells/ h. Increasing the glutamine concentrations of minimum essential medium to 4 mM increased ammonia production to slightly greater than 30 nmol/10(6) cells/ h. Increasing the media concentration of glutamate, glycine, or asparagine resulted in no significant increase in ammoniagenesis. Analysis of media amino acid concentration revealed that glutamine was the main amino acid consumed while alanine was the predominant amino acid produced. The glutaminase activity of these cells appears to be primarily phosphate-dependent, similar to that observed in vitro in papillary tubules. Alterations of K+ or H+ ion concentration did not alter ammoniagenesis, but addition of 2.5 mM ammonium chloride significantly reduced net ammonia production. It is concluded that rat papillary epithelial cells have the intrinsic ability to utilize glutamine to generate ammonia and alanine. In vivo ammonia produced locally in the medulla may contribute to final urinary ammonium excretion.
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PMID:Ammonia production and amino acid metabolism by rat renal papillary epithelial cells in culture. 396 60

The biochemical and morphological extent of glycoprotein synthesis inhibition of cellular and extracellular proteins was studied on cultured renal collecting duct (CD) epithelium. We found that tunicamycin (4 micrograms/ml) inhibits the glycosylation of a 150,000 d glycoprotein (gpCDI). A 85,000 d glycoprotein (gpCDII) was not affected. The inhibition by tunicamycin demonstrates that gpCDI has characteristics of a N-glycan, whereas gpCDII seems to be an O-glycan. 6-diazo-5-oxo-norleucine (4 X 10(-5) M) which was used as glutamine analogue, did not show a comparable inhibitory effect as seen with tunicamycin. The lack of effect of norleucine demonstrates that glutamine is not the locus of glycosylation in both proteins. However, because of the tunicamycin inhibition it points to asparagine as the site of glycosylation in the gpCDI. Long term cultures of the tissue up to 15 days in the presence of tunicamycin and norleucine and of substances usually used as basement membrane inhibitors, such as hydroxy-D-proline (1 mM), L-azetidine-2-carboxylic acid (1 mM) and o- and p-nitrophenyl-xylopyranoside 1 mM), revealed that it is possible to eliminate completely the fibroblasts beneath the cultured epithelium and within the degenerating corematerial. Experiments with hydroxy-D-proline showed the most striking effect. Experiments with L-azetidine-2-carboxylic acid and nitrophenyl-xylopyranoside resulted in the elimination of fibroblasts and dedifferentiation of the collecting duct epithelium.
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PMID:Effects of glycoprotein and basement membrane synthesis inhibitors on the growth of cultured renal collecting duct epithelium. 648 Apr 14

Aquaporin-2 (AQP-2) is a vasopressin-regulated water channel in the kidney collecting duct. AQP-2 is selectively permeable to water molecule and is translocated between the apical membrane and subapical endosomes in response to vasopressin. To investigate the localization and structure of the aqueous pathway of the AQP-2 water channel, a series of site-directed mutants was constructed and functionally analyzed. Insertion of N-glycosylation reporter sequence into each hydrophilic loop (HL) indicated that AQP-2 has a six-membrane spanning topology and that insertional mutations in HL-2 or HL-5 do not alter water channel function. Mercury-sensitive site of AQP-2 is located near the second asparagine-proline-alanine (NPA) domain at cysteine 181, but not near the first NPA domain. Replacement of HL-3 or HL-4 with the corresponding part of Escherichia coli glycerol facilitator abolished water channel function without changing plasma membrane expression of the channel protein. Introduction of cysteine residues in His-122, Asn-123, Gly-154, Asp-155, or Asn-156 induced partial mercury sensitivity, and point mutations in asparagine 123 significantly altered water permeability. Our results implicate that the structure of AQP-2 is different from models previously proposed for AQP-1 and that HL-3 and HL-4 are closely located to the aqueous pathway.
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PMID:Structure of aquaporin-2 vasopressin water channel. 861 98

Nephrogenic diabetes insipidus (NDI) is associated with germline mutations in two genes: vasopressin receptor type 2 (V2(R)) in X-linked NDI, and the water channel aquaporin-2, in autosomal-recessive disease. Genetic heterogeneity is further emphasized by reports of phenotypically abnormal individuals with normal structural genes. We analyzed both genes in five Brazilian families and the aquaporin-2 gene in two Swedish families with clinical and laboratory diagnosis of NDI, by a combination of denaturing gradient gel electrophoresis (DGGE) and direct DNA sequencing. A novel polymorphism in the aquaporin-2 gene (S167S), but no disease-associated mutations in any tested individual from all seven families, was detected. In two Brazilian families, frameshift mutations were detected in the V2(R) gene: one leading to a premature stop after codon 36 and the other to a longer peptide (462 aa instead of the 373 aa wild-type protein). In two other Brazilian families, probable disease-associated missense mutations were detected: an alanine to proline at codon 163 (A163P) and an asparagine to aspartic acid at codon 85 (D85N). In one Brazilian family, both genes were structurally normal and the aquaporin-2 gene was also normal in the two Swedish kindreds. This report further extends the mutational spectrum of NDI and suggests that there are other mutational or epigenetic events inactivating the two known genes or even novel genes that underlie NDI.
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PMID:Molecular analyses of the vasopressin type 2 receptor and aquaporin-2 genes in Brazilian kindreds with nephrogenic diabetes insipidus. 1047 31

Both mammals and birds can concentrate urine hyperosmotic to plasma via a countercurrent multiplier mechanism, although evolutionary lines leading to mammals and birds diverged at an early stage of tetrapod evolution. We reported earlier (Nishimura H, Koseki C, and Patel TB. Am J Physiol Regul Integr Comp Physiol 271: R1535-R1543, 1996) that arginine vasotocin (AVT; avian antidiuretic hormone) increases diffusional water permeability in the isolated, perfused medullary collecting duct (CD) of the quail kidney. In the present study, we have identified an aquaporin (AQP) 2 homolog water channel in the medullary cones of Japanese quail, Coturnix coturnix (qAQP2), by RT-PCR-based cloning techniques. A full-length cDNA contains an 822-bp open reading frame that encodes a 274-amino acid sequence with 75.5% identity to rat AQP2. The qAQP2 has six transmembrane domains, two asparagine-proline-alanine (NPA) sequences, and putative N-glycosylation (asparagine-124) and phosphorylation sites (serine-257) for cAMP-dependent protein kinase. qAQP2 is expressed in the membrane of Xenopus laevis oocytes and significantly increased its osmotic water permeability (P(f)), inhibitable (P < 0.01) by mercury chloride. qAQP2 mRNA (RT-PCR) was detected in the kidney; medullary mRNA levels were higher than cortical levels. qAQP2 protein that binds to rabbit anti-rat AQP2 antibody is present in the apical/subapical regions of both cortical and medullary CDs from normally hydrated quail, and the intensity of staining increased only in the medullary CDs after water deprivation or AVT treatment. The relative density of the approximately 29-kDa protein band detected by immunoblot from the medullary cones was modestly higher in water-deprived/AVT-treated quail. The results suggest that 1) medullary CDs of quail kidneys express a mercury-sensitive functioning qAQP2 water channel, and 2) qAQP2 is at least partly regulated by an AVT-dependent mechanism. This is the first clear identification of AQP2 homolog in nonmammalian vertebrates.
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PMID:Molecular and functional characterization of a vasotocin-sensitive aquaporin water channel in quail kidney. 1520 86