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)

The Na+-H+ exchanger NHE3 and the thiazide-sensitive Na+-Cl- cotransporter NCC are the major apical sodium transporters in the proximal convoluted tubule and the distal convoluted tubule of the kidney, respectively. We investigated the mechanism of compensation that allows maintenance of sodium balance in NHE3 knockout mice and in NCC knockout mice. We used a so-called 'targeted proteomics' approach, which profiles the entire renal tubule with regard to changes in Na+ transporter and aquaporin abundance in response to the gene deletions. Specific antibodies to the Na+ transporters and aquaporins expressed along the nephron were utilized to determine the relative abundance of each transporter. Semiquantitative immunoblotting was used which gives an estimate of the percentage change in abundance of each transporter in knockout compared with wild-type mice. In NHE3 knockout mice three changes were identified which could compensate for the loss of NHE3-mediated sodium absorption. (a) The proximal sodium-phosphate cotransporter NaPi-2 was markedly upregulated. (b) In the collecting duct, the 70 kDa form of the y-subunit of the epithelial sodium channel, ENaC, exhibited an increase in abundance. This is thought to be an aldosterone-stimulated form of y-ENaC. (c) Glomerular filtration was significantly reduced. In the NCC knockout mice, amongst all the sodium transporters expressed along the renal tubule, only the 70 kDa form of the y-subunit of the epithelial sodium channel, ENaC, exhibited an increase in abundance. In conclusion, both mouse knockout models demonstrated successful compensation for loss of the deleted transporter. More extensive adaptation occurred in the case of the NHE3 knockout, presumably because NHE3 is responsible for much more sodium absorption in normal mice than in NCC knockout mice.
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PMID:Profiling of renal tubule Na+ transporter abundances in NHE3 and NCC null mice using targeted proteomics. 1115 68

Diabetes mellitus (DM) is associated with osmotic diuresis and natriuresis. At day 15, rats with DM induced by streptozotocin (n = 13) had severe hyperglycemia (27.1 +/- 0.4 vs. 4.7 +/- 0.1 mM in controls) and had a fivefold increase in water intake (123 +/- 5 vs. 25 +/- 2 ml/day) and urine output. Semiquantitative immunoblotting revealed a significant increase in inner medullary AQP2 (201 +/- 12% of control rats, P < 0.05) and phosphorylated (Ser(256)) AQP2 (p-AQP2) abundance (299 +/- 32%) in DM rats. Also, the abundance of inner medullary AQP3 was markedly increased to 171 +/- 19% of control levels (100 +/- 4%, n = 7, P < 0.05). In contrast, the abundance of whole kidney AQP1 (90 +/- 3%) and inner medullary AQP4 (121 +/- 16%) was unchanged in rats with DM. Immunoelectron microscopy further revealed an increased labeling of AQP2 in the apical plasma membrane of collecting duct principal cells (with less labeling in the intracellular vesicles) of DM rats, indicating enhanced trafficking of AQP2 to the apical plasma membrane. There was a marked increase in urinary sodium excretion in DM. Only Na(+)/H(+) exchanger NHE3 was downregulated (67 +/- 10 vs. 100 +/- 11%) whereas there were no significant changes in abundance of type 2 Na-phosphate cotransporter (128 +/- 6 vs. 100 +/- 10%); the Na-K-2Cl cotransporter (125 +/- 19 vs. 100 +/- 10%); the thiazide-sensitive Na-Cl cotransporter (121 +/- 9 vs. 100 +/- 10%); the alpha(1)-subunit of the Na-K-ATPase (106 +/- 7 vs. 100 +/- 5%); and the proximal tubule Na-HCO(3) cotransporter (98 +/- 16 vs. 100 +/- 7%). In conclusion, DM rats had an increased AQP2, p-AQP2, and AQP3 abundance as well as high AQP2 labeling of the apical plasma membrane, which is likely to represent a vasopressin-mediated compensatory increase in response to the severe polyuria. In contrast, there were no major changes in the abundance of AQP1, AQP4, and several major proximal and distal tubule Na(+) transporters except NHE3 downregulation, which may participate in the increased sodium excretion.
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PMID:Compensatory increase in AQP2, p-AQP2, and AQP3 expression in rats with diabetes mellitus. 1124 63

In assessing disorders of potassium excretion, urine composition is used to calculate the transtubular gradient (TTKG), as an estimate of tubule fluid concentration, at a point when the fluid was last isotonic to plasma, namely, within the cortical collecting duct (CCD). A mathematical model of the CCD has been developed, consisting of principal cells and alpha- and beta-intercalated cells, and which includes Na(+), K(+), Cl(-), HCO, CO(2), H(2)CO(3), phosphate, ammonia, and urea. Parameters have been selected to achieve fluxes and permeabilities compatible with data obtained from perfusion studies of rat CCD under the influence of both antidiuretic hormone and mineralocorticoid. Both epithelial (flat sheet) and tubule models have been configured, and model calculations have focused on the determinants of the TTKG. Using the epithelial model, luminal K(+) concentrations can be computed at which K(+) secretion ceases (0-flux equilibrium), and this luminal concentration derives from the magnitude of principal cell peritubular uptake of K(+) via the Na-K-ATPase, relative to principal cell peritubular membrane K(+) permeability. When the model is configured as a tubule and examined in the context of conditions in vivo, osmotic equilibration of luminal fluid produces a doubling of the initial K(+) concentration, which, depending on delivered load, may be substantially greater than the zero-flux equilibrium value. Under such circumstances, the CCD will be a site for K(+) reabsorption, although the relatively low permeability ensures that this reabsorptive flux is likely to be small. Osmotic equilibration may also raise luminal NH(3) concentrations well above those in cortical blood. In this situation, diffusive reabsorption of NH(3) provides a mechanism for base reclamation without the metabolic cost of active proton secretion.
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PMID:A mathematical model of rat cortical collecting duct: determinants of the transtubular potassium gradient. 1135 47

Using a standardised procedure, we assessed the crystallisation properties of calcium phosphate in urine with a composition matching that in the distal part of the distal tubules (DTd) and of calcium oxalate in urine with a composition matching that in the mid-collecting duct (CDm). We used 8-h urine samples collected between 2200 h and 0600 h with sodium azide as preservative. Urine from ten patients with recurrent CaOx stone formation and from ten normal subjects was used for the measurements. The DTd and CDm samples were obtained by diluting the voided 8-h urine to 3000 ml and 1750 ml per 1.73 m2 body surface area, respectively. The nucleation was studied in DTd urine following supersaturation with CaP. The crystal size distribution was assessed with a Coulter counter both following supersaturation of DTd urine with CaP and of CDm urine with CaOx. The crystallisation of CaP in DTd urine as well as that of CaOx in CDm urine, in the presence of CaP crystals that had been precipitated in DTd urine, was measured with the isotope technique. The inhibition of CaOx and brushite crystal aggregation in standardised diluted aliquots of DTd and CDm urine was assessed spectrophotometrically as the rate of sedimentation. There was a slightly increased sedimentation rate and a lower initial absorbance in DTd urine from stone formers supersaturated with CaP. Although these findings might reflect a state of increased crystal aggregation in stone formers' urine, this could not be confirmed by crystal size measurements in the Coulter counter. The inhibition of brushite crystal aggregation in DTd urine was significantly in stone formers' urine than in normal subjects' urine (P < 0.001). Moreover, all inhibition values in DTd samples from stone formers were negative, suggesting a promoter effect on crystal aggregation. The inhibition of CaOx crystal aggregation in CDm urine also was significantly higher in CDm urine from normal subjects than in CDm urine from stone formers (P < 0.05). For all other variables the level was similar when urine samples from the two groups were compared. Although this series of crystallisation assessments was carried out on a small number of standardised diluted urine samples only, the results nevertheless emphasise a defect in aggregation inhibition as one important determinant for an abnormal calcium salt crystallisation in patients with recurrent stone formations. This difference obviously includes aggregation of both CaP crystals in DTd urine and CaOx crystals in CDm urine. The results also show that assessment of crystallisation properties of this kind can be carried out in standardised, diluted 8-h night urine samples, which accordingly can be used in the routine work-up of patients with calcium stone disease. Such an approach might prove useful in order to get information on the combined effects of the driving force of supersaturation and crystallisation modifying properties accomplished by urinary macromolecules and other modifying agents.
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PMID:Crystallisation properties in stone forming and normal subjects' urine diluted using a standardised procedure to match the composition of urine in the distal part of the distal tubule and the middle part of the collecting duct. 1139 32

The opioid receptor antagonist, naloxone, has been shown to have beneficial effects in the kidney and to be implicated in renal salt and water balance. In the present study the signal transduction pathways utilized by naloxone were studied in an epithelial cell line model of the cortical collecting duct, A6 cells. We found that naloxone has a dual effect depending on the concentration used: at a low concentration (10(-6) M) it antagonized the beta-endorphin-dependent increase in cytoplasmic calcium [Ca(2+)](i), while at higher concentrations (>10(-5) M) it increased [Ca(2+)](i) and intracellular inositol phosphate levels. While naloxone-induced increases in [Ca(2+)](i) occurred in the absence of external calcium, it was significantly stimulated by increasing the external calcium concentration, suggesting that naloxone increases [Ca(2+)](i) via both calcium release and calcium influx. In polarized A6 cell monolayers naloxone inhibited the activity of the Na(+)/H(+) exchanger (NHE) only when added to the basolateral cell surface. This inhibition of the NHE was prevented by pretreatment of the cells with either the intracellular calcium chelator, BAPTA or with the protein kinase C inhibitor, calphostin C. These findings demonstrate that naloxone induces a rapid increase in intracellular calcium which inhibits the NHE via the calcium-dependent protein kinase C regulatory pathway.
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PMID:Naloxone inhibits A6 cell Na(+)/H(+) exchange by activating protein kinase C via the mobilization of intracellular calcium. 1154 52

A mathematical model of the rat collecting duct (CD) is used to examine the effect of delivered load of bicarbonate and nonbicarbonate buffer on urinary acidification. Increasing the delivered load of HCO(3)(-) produces bicarbonaturia, and, with luminal carbonic anhydrase absent, induces a disequilibrium luminal pH and a postequilibration increase in urinary PCO2. At baseline flows, this disequilibrium disappears when luminal carbonic anhydrase rate coefficients reach 1% of full catalysis. The magnitude of the equilibration PCO2 depends on the product of urinary acid phosphate concentration and the disequilibrium pH. Thus, although increasing phosphate delivery to the CD decreases the disequilibrium pH, the increase in urinary phosphate concentration yields an overall increase in postequilibration PCO2. In simulations of experimental HCO(3)(-) loading in the rat, model predictions of urinary PCO2 exceed the measured PCO2 of bladder urine. In part, the higher model predictions for urinary PCO2 may reflect higher urinary flow rates and lower urinary phosphate concentrations in the experimental preparations. However, when simulation of CD function during HCO(3)(-) loading acknowledges the high ambient renal medullary PCO2 (5), the predicted urinary PCO2 of the model CD is yet that much greater. This discrepancy cannot be resolved within the model but requires additional experimental data, namely, concomitant determination of urinary buffer concentrations within the tubule fluid sampled for PCO2 and pH. This model should provide a means for simulating formal testing of urinary acidification and thus for examining hypotheses regarding transport defects underlying distal renal tubular acidosis.
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PMID:A mathematical model of rat collecting duct. II. Effect of buffer delivery on urinary acidification. 1238 79

Defects in an intracellular chloride channel CLC-5 cause Dent's disease, an inherited kidney stone disorder. Using a collecting duct model, mIMCD-3 cells, we show expression of dimeric mCLC-5. Transient transfection of antisense CLC-5 reduces CLC-5 protein expression. Binding of both calcium phosphate (hydroxyapatite) and calcium oxalate monohydrate (COM) crystals overlaid onto mIMCD-3 cultures was affected by altered CLC-5 expression. Calcium phosphate crystal agglomerations (>10 microm) were minimal in control (9%) and sense (13%) CLC-5-transfected cells, compared to 66% of antisense CLC-5-transfected cells (P<0.001). Small calcium phosphate crystals (<10 microm) were found associated with 45% of sense CLC-5-treated cells, of which the majority (11/14 cells) appeared to be internalised within the cell. Calcium oxalate agglomerations (>10 microm) were also largely absent for controls or sense mCLC-5 transfectants (11% and 9% of cells, respectively) with COM crystal agglomerates predominating in antisense CLC-5 transfectants (66%, P<0.0001). We conclude that collecting duct cells with reduced CLC-5 expression lead to a tendency to form calcium crystal agglomeration, which may help explain the nephrocalcinosis and nephrolithiasis seen in Dent's disease.
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PMID:Calcium phosphate and calcium oxalate crystal handling is dependent upon CLC-5 expression in mouse collecting duct cells. 1515 17

Renal distribution and function of TWIK-1, a member of the two-pore-domain potassium channel family, was studied in mouse kidney. TWIK-1 is expressed in apical and subapical localizations of proximal tubule and cytoplasmic sites of thin and thick ascending limbs, distal convoluted tubules and medullary collecting duct. Studies in mice lacking intact TWIK-1 (twik-1 -/-) and wild-type mice (twik-1 +/+) revealed an attenuated ability to increase renal phosphate (Pi) reabsorption and stabilize plasma Pi concentration in response to a low Pi diet in twik-1 -/- mice. Western blot analysis and immunohistochemistry for the electrogenic 3Na(+)-1HPO(4) (2-)-cotransporter NaPi-2a revealed a reduced reno-cortical expression in twik-1 -/- mice under these conditions. Under normal diet, twik-1 -/- mice presented lower urinary flow rates. Acute pharmacologic blockade of the vasopressin V(2)-receptor revealed both an attenuated diuretic response and an attenuated internalization of aquaporin-2 in the inner medullary collecting duct in twik-1 -/- versus +/+ mice. In summary, mice deficient for TWIK-1 presented impaired regulation of (i) Pi transport in proximal tubule and (ii) water transport in medullary collecting duct. TWIK-1 may contribute to membrane trafficking/expression of transport molecules in proximal tubule and medullary collecting duct, and possibly other renal sites of expression.
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PMID:Expression and insights on function of potassium channel TWIK-1 in mouse kidney. 1602

A novel murine glycerol-3-phosphate acyltransferase-like protein 1 (named xGPAT1) has been cloned. The mouse xGPAT1 gene is located on mouse Chromosome 2, spans >19 kb, and consists of at least 23 exons. The protein is 32% identical and 72% similar to mouse mitochondrial GPAT (mtGPAT) on the amino acid level. Sequencing analysis confirmed that xGPAT1 has a 2403-bp open reading frame (ORF) that encodes an 801-amino acid protein with an estimated molecular mass of 89.1 kDa. A hydropathy plot of the deduced xGPAT1 protein showed a high degree of similarity with that of the mtGPAT protein. Using 5'-rapid amplification of cDNA ends, two alternate, untranslated exon 1 (1a and b) isoforms were obtained, generating variants xGPAT1-v1 and xGPAT1-v2. xGPAT1-v1 is expressed in mouse heart, liver, spleen, kidney and murine inner medullary collecting duct 3 (mIMCD3) cells, while xGPAT1-v2 is expressed in mouse liver, spleen, kidney, white and brown adipose tissues and 3T3-L1 pre- and post-adipocytes. xGPAT1 was distributed in the membrane fraction and showed GPAT activity when epitope-tagged xGPAT1 was expressed in Chinese hamster ovary (CHO)-K1 cells.
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PMID:Molecular cloning of a murine glycerol-3-phosphate acyltransferase-like protein 1 (xGPAT1). 1701 44

Hypothyroidism in humans is associated with incomplete distal renal tubular acidosis, presenting as the inability to respond appropriately to an acid challenge by excreting less acid. Here, we induced hypothyroidism in rats with methimazole (HYPO) and in one group substituted with l-thyroxine (EU). After 4 wk, acid-base status was similar in both groups. However, after 24 h acid loading with NH(4)Cl HYPO rats displayed a more pronounced metabolic acidosis. The expression of the Na(+)/H(+) exchanger NHE3, the Na(+)-phosphate cotransporter NaPi-IIa, and the B2 subunit of the vacuolar H(+)-ATPase was reduced in the brush-border membrane of the proximal tubule of the HYPO group, paralleled by a lower abundance of the Na(+)/HCO(3)(-) cotransporter NBCe1 and a higher expression of the acid-secretory type A intercalated cell-specific Cl(-)/HCO(3)(-) exchanger AE1. In contrast to control conditions, the expression of NBCe1 was increased in the HYPO group during metabolic acidosis. In addition, net acid excretion was similar in both groups. The relative number of type A intercalated cells was increased in the connecting tubule and cortical collecting duct of the HYPO group during acidosis. Thus thyroid hormones modulate the renal response to an acid challenge and alter the expression of several key acid-base transporters. Mild hypothyroidism is associated only with a very mild defect in renal acid handling, which appears to be mainly located in the proximal tubule and is compensated by the distal nephron.
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PMID:Thyroid hormone deficiency alters expression of acid-base transporters in rat kidney. 1740 79


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