Angiotensin II stimulates trafficking of NHE3, NaPi2, and associated proteins into the proximal tubule microvilli. (57/75)

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Sex differences in adaptive downregulation of pre-macula densa sodium transporters with ANG II infusion in mice. (58/75)

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Immunohistochemical analyses of parathyroid hormone-dependent downregulation of renal type II Na-Pi cotransporters by cryobiopsy. (59/75)

The "in vivo cryotechnique" (IVCT) is a new method of morphological analysis which has the advantage of freezing tissues in living animals without stopping their blood circulation. The purpose of this study was to investigate the effect of parathyroid hormone (PTH) on renal type II Na-Pi transporters (NaPi-IIa and NaPi-IIc) and "cryobiopsy" (CB) using special cryoforceps as a simple method of the IVCT. The kidney tissues were biopsied at various time points after PTH administration by CB using liquid nitrogen as the cryogen. By hematoxylin-eosin (HE) staining the kidney tissues, well-frozen areas without visible ice crystals were obtained in the tissue surface areas, and the brush border membrane (BBM) of proximal tubules was well preserved at a light microscopic level. Immunohistochemical evaluation showed that PTH downregulated NaPi-IIa and NaPi-IIc at the BBM, being controlled by a different mechanism. In this method, the PTH-induced internalization of NaPi-IIc from microvilli to subapical compartments was not observed in the tissue preparations. NaPi-IIc protein appears to be degraded in microvilli of the proximal tubular cells after the injection of PTH. We suggest that CB using liquid nitrogen is useful to investigate renal type II Na-Pi transporters at the light microscopic level.  (+info)

Lithium interactions with Na+-coupled inorganic phosphate cotransporters: insights into the mechanism of sequential cation binding. (60/75)

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Genetic disorders of phosphate regulation. (61/75)

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FGF23-induced hypophosphatemia persists in Hyp mice deficient in the WNT coreceptor Lrp6. (62/75)

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Expression of a renal type I sodium/phosphate transporter (NaPi-1) induces a conductance in Xenopus oocytes permeable for organic and inorganic anions. (63/75)

Two distinct molecular types (I and II) of renal proximal tubular brush border Na+/Pi cotransporters have been identified by expression cloning on the basis of their capacity to induce Na+-dependent Pi influx in tracer experiments. Whereas the type II transporters (e.g., NaPi-2 and NaPi-3) resemble well known characteristics of brush border Na+/Pi cotransport, little is known about the properties of the type I transporter (NaPi-1). In contrast to type II, type I transporters produced electrogenic transport only at high extracellular Pi concentrations (> or =3 mM). On the other hand, expression of NaPi-1 induced a Cl- conductance in Xenopus laevis oocytes, which was inhibited by Cl- channel blockers [5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) > niflumic acid >> 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid]. Further, the Cl- conductance was inhibited by the organic anions phenol red, benzylpenicillin (penicillin G), and probenecid. These organic anions induced outwardly directed currents in the absence of Cl-. In tracer studies, we observed uptake of benzylpenicillin with a Km of 0.22 mM; benzylpenicillin uptake was inhibited by NPPB and niflumic acid. These findings suggest that the type I Na+/Pi cotransporter functions also as a novel type of anion channel permeable not only for Cl- but also for organic anions. Such an apical anion channel could serve an important role in the transport of Cl- and the excretion of anionic xenobiotics.  (+info)

Structure of murine and human renal type II Na+-phosphate cotransporter genes (Npt2 and NPT2). (64/75)

Na+-phosphate (Pi) cotransport across the renal brush border membrane is the rate limiting step in the overall reabsorption of filtered Pi. Murine and human renal-specific cDNAs (NaPi-7 and NaPi-3, respectively) related to this cotransporter activity (type II Na+-Pi cotransporter) have been cloned. We now report the cloning and characterization of the corresponding mouse (Npt2) and human (NPT2) genes. The genes were cloned by screening mouse genomic and human chromosome 5-specific libraries, respectively. Both genes are approximately 16 kb and are comprised of 13 exons and 12 introns, the junctions of which conform to donor and acceptor site consensus sequences. Putative CAAT and TATA boxes are located, respectively, at positions -147 and -40 of the Npt2 gene and -143 and -51 of the NPT2 gene, relative to nucleotide 1 of the corresponding cDNAs. The translation initiation site is within exon 2 of both genes. The first 220 bp of the mouse and human promoter regions exhibit 72% identity. Two transcription start sites (at positions -9 and - 10 with respect to nucleotide 1 of NaPi-7 cDNA) and two polyadenylylation signals were identified in the Npt2 gene by primer extension, 5' and 3' rapid amplification of cDNA ends (RACE). A 484-bp 5' flanking region of the Npt2 gene, comprising the CAAT box, TATA box, and exon 1, was cloned upstream of a luciferase reporter gene; this construct significantly stimulated luciferase gene expression, relative to controls, when transiently transfected into OK cells, a renal cell line expressing type II Na+ -Pi cotransporter activity. The present data provide a basis for detailed analysis of cis and trans elements involved in the regulation of Npt2/NPT2 gene transcription and facilitate screening for mutations in the NPT2 gene in patients with autosomally inherited disorders of renal Pi reabsorption.  (+info)