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Results for “Kidney Tubules, Distal”

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At least 19 recordsLinked to original sources
PubMed1983

Metabolic heterogeneity of the proximal and distal kidney tubules.

Proximal and distal tubule suspensions were prepared from kidneys of Sprague-Dawley rats by an isolation procedure on a Percoll gradient. The marker enzymes alkaline phosphatase (brush border) and hexokinase (cytoplasmic) as well as p-aminohippurate transport capacity, gluconeogenic activity and electron microscopy were used to characterize the two kidney tubule suspensions. The results of this study indicate that cytochrome P-450 is localized to the proximal tubular cells and that the O-deethylation of 7-ethoxycoumarin was higher in the proximal than distal fraction. Both proximal and distal tubules showed glucuronidation and deacetylation capacities and a relatively equal distribution of non-protein sulfhydryls. These studies demonstrate metabolic heterogeneity of the nephron, the proximal tubule being the main site of renal xenobiotic metabolism. Understanding of metabolic heterogeneity of proximal and distal kidney tubules should provide important information regarding cell specific mechanisms of nephrotoxicity.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1982

The MDCK epithelial cell line expresses a cell surface antigen of the kidney distal tubule.

Monoclonal antibodies were prepared against the Madin-Darby canine kidney (MDCK) cell line to identify epithelial cell surface macromolecules involved in renal function. Lymphocyte hybrids were generated by fusing P3U-1 myeloma cells with spleen cells from a C3H mouse immunized with MDCK cells. Hybridomas secreting anti-MDCK antibodies were obtained and clonal lines isolated in soft agarose. We are reporting on one hybridoma line that secretes a monoclonal antibody that binds to MDCK cells at levels 20-fold greater than background binding. Indirect immunofluorescence microscopy was utilized to study the distribution of antibody binding on MDCK cells and on frozen sections of dog kidney and several nonrenal tissues. In the kidney the fluorescence staining pattern demonstrates that the antibody recognizes an antigenic determinant that is expressed only on the epithelial cells of the thick ascending limb of Henle's loops and the distal convoluted tubule and appears to be localized on the basolateral plasma membrane. This antigen also has a unique distribution in non-renal tissues and can only be detected on cells known to be active in transepithelial ion movements. These results indicate the probable distal tubule origin of MDCK and suggest that the monoclonal antibody recognizes a cell surface antigen involved in physiological functions unique to the kidney distal tubule and transporting epithelia of nonrenal tissues.

Animals↗
PubMed1987

Monoclonal antibodies to human erythrocyte membrane Ca++-Mg++ adenosine triphosphatase pump recognize an epitope in the basolateral membrane of human kidney distal tubule cells.

Human calcium transporting tissues were examined to determine whether they contained a protein similar to the Ca++-Mg++ adenosine triphosphatase (Ca++-Mg++ATPase) pump of the human erythrocyte membrane. Tissues were processed for immunoperoxidase staining using monoclonal antibodies against purified Ca++-Mg++ATPase. In human kidneys, specific staining was found only along the basolateral membrane of the distal convoluted tubules. Glomeruli and other segments of the nephron did not stain. Staining of erythrocytes in human spleen was readily observed. Human small intestine, human parathyroid, and human liver showed no antigens that crossreacted with the antibodies to Ca++-Mg++ATPase. Specific staining of distal tubule basolateral membranes from the kidney of a chimpanzee was also noted. Our experiments show, for the first time, that basolateral membranes of the human distal convoluted tubule contain a protein that is immunologically similar to the human erythrocyte Ca++-Mg++ATPase. These observations suggest that the cells of the distal convoluted tubules of human kidney may have a calcium pump similar to that of human erythrocyte membranes.

Animals↗
PubMed1980

Localization of Na+, K+ -ATPase to the inside of the basolateral cell membranes of epithelial cells of proximal and distal tubules in rabbit kidney.

Cysteine-sensitive alkaline phosphatase and/or ouabain-sensitive Na+, K+ -ATPase were studied by ultrastructure cytochemistry in epithelial cells of proximal and distal kidney tubules. Alkaline phosphatase reactivity was confined to the surface of the microvillous luminal cell membrane of proximal tubule cells, whereas distal tubules and collecting ducts were unreactive. The Na+, K+- ATPase reactivity was localized evenly along the cytoplasmic side of the basolateral cell membrane of cells of proximal and distal tubules and in collecting ducts. In the proximal tubules, where the activity was strongest, the Na+, K+- ATPase deposits were also found in the 10--50 nm gap between the cell membrane and the cisternae of tubulo-cisternal endoplasmic reticulum (TER) underlying a major part of the basolateral cell membrane. The restriction of NA+, K+ -ATPase sites, which are involved in extrusion of Na+ from the cell, to a narrow cytoplasmic compartment located between the cell membrane and the cisternae of TER, is consistent with a transport role for the TER.

Animals↗
PubMed2003

Estrogen and androgen regulation of plasma membrane calcium pump activity in immortalized distal tubule kidney cells.

The ATP dependent plasma membrane calcium pump (PMCA) is a regulator of renal calcium reabsorption. The effect of estrogen and dihydrotestosterone to increase the activity of the PMCA in membrane vesicle preparations from a distal tubule cell line was investigated. 17beta Estradiol (10(-10)M) increased PMCA activity (1.5 +/- 0.2-fold increase compared to control) with 24 h, but not 1 or 5 h, of exposure, an effect that was blocked by the addition of the estrogen antagonist ICI 164384. alpha Estradiol did not increase PMCA activity. Dihydrotestosterone (10(-11)M ) resulted in a dose dependent increase in PMCA activity (1.5+/-0.1-fold increase compared to control) with 24h, but not 1 or 5h, of exposure, an effect that was blocked by the androgen receptor agonist flutamide. Testosterone (10(-5)M) also increased PMCA activity (1.9+/-0.3-fold increase compared to control). Neither estrogen nor dihydrotestosterone increased PMCA protein expression in MDBK cells, indicating that these hormones increase PMCA activity by regulating PMCA activity rather than PMCA expression. These results demonstrate receptor dependent stimulatory effects of both estrogen and dihydrotestosterone to increase PMCA activity. and have significance for our understanding of estrogen and androgen deficient states on calcium transport.

Androgen Antagonists↗
PubMed2000

pH and external Ca(2+) regulation of a small conductance Cl(-) channel in kidney distal tubule.

A single channel characterization of the Cl(-) channels in distal nephron was undertaken using vesicles prepared from plasma membranes of isolated rabbit distal tubules. The presence in this vesicle preparation of ClC-K type Cl(-) channels was first established by immunodetection using an antibody raised against ClC-K isoforms. A ClC-K1 based functional characterization was next performed by investigating the pH and external Ca(2+) regulation of a small conductance Cl(-) channel which we identified previously by channel incorporation experiments. Acidification of the cis (external) solution from pH 7.4 to 6.5 led to a dose-dependent inhibition of the channel open probability P(O). Similarly, changing the trans pH from 7.4 to 6.8 resulted in a 4-fold decrease of the channel P(O) with no effect on the channel conductance. Channel activity also appeared to be regulated by cis (external) Ca(2+) concentration, with a dose-dependent increase in channel activity as a function of the cis Ca(2+) concentration. It is concluded on the basis of these results that the small conductance Cl(-) channel present in rabbit distal tubules is functionally equivalent to the ClC-K1 channel in the rat. In addition, the present work constitutes the first single channel evidence for a chloride channel regulated by external Ca(2+).

Animals↗
PubMed1986

Dependence of oxygen consumption on Cl- transport and metabolic substrates in the early distal tubule of the Triturus kidney.

The early distal tubule (eDT) and the proximal tubule (PT) were dissected as tissue samples from the Triturus kidney. The oxygen consumption (QO2) of these tubules was measured and the effects on QO2 by transport inhibitors and metabolic substrates were studied. In eDT, complete Cl- replacement with NO3- or an addition of furosemide (2 X 10(-5) M) reduced Qo2 from 8.4 +/- 1.7 to 4.4 +/- 0.8 or from 8.3 +/- 1.6 to 4.4 +/- 0.6 nl X min-1 X mg-1 (dry weight), respectively. Also Na+ replacement with choline or with an addition to ouabain (1 X 10(-3) M) reduced QO2 from 5.9 +/- 0.8 to 3.4 +/- 0.4 or from 13.2 +/- 1.8 to 4.7 +/- 0.3 nl X min-1 X mg-1 (dry weight), respectively. In PT, complete Cl- replacement with NO3- or the addition of furosemide did not affect QO2 significantly, but Na+ replacement with choline or the addition of ouabain reduced it from 8.1 +/- 1.0 to 5.4 +/- 0.7 or from 10.8 +/- 0.9 to 7.4 +/- 0.8 nl X min-1 X mg-1 (dry weight), respectively. The data indicate that about a half of the QO2 in eDT is linked to active Cl- transport, in PT, Cl- is not transported actively and is not affected by furosemide. Effects on QO2 by various metabolic substrates, including TCA-cycle intermediates and metabolizable amino acids and carboxylic acids were tested. Among them, succinate, L-glutamate, L-aspartate, citrate, and acetate were found to effectively increase the QO2. The substrate-dependencies of QO2 in eDT were very similar to those in PT, in kinds of effective substrates and in the extent of increase. These findings suggest that, in eDT and PT, the uptake mechanisms for substrates and their coupling with aerobic metabolism are very similar.

Amino Acids↗
PubMed1989

Plasma membrane calcium pump and 28-kDa calcium binding protein in cells of rat kidney distal tubules.

In an effort to extend our studies on Ca2+ pumps to animal models, we developed a new monoclonal antibody (5F10) prepared against the human erythrocyte Ca2+-Mg2+-adenosinetriphosphatase (ATPase) that recognizes a protein of approximately 140 kDa in rat kidney homogenates. Enzyme-linked immunosorbent assays show that monoclonal antibody 5F10 binds purified Ca2+-Mg2+-ATPase and rat kidney membrane extracts in a concentration-dependent manner. In paraffin-embedded tissue sections, antibody 5F10 binds to an epitope in the basolateral membranes of rat kidney distal convoluted tubule principal cells. The antibody does not bind to intercalated cells. The latter cells were characterized by the presence of large amounts of carbonic anhydrase C. Polyclonal antibodies directed against chick intestinal 28-kDa vitamin D-dependent calcium binding protein (28-kDa CaBP) also bind epitopes in distal convoluted tubule cells, connecting tubules, and portions of collecting duct but not intercalated cells. Western blot and 45Ca blot analysis of renal cytosolic proteins showed that the polyclonal 28-kDa CaBP-directed antibody detects a protein which also binds calcium. Western blot analysis with monoclonal antibody 5F10 shows binding to both the authentic purified erythrocyte Ca2+ pump (approximately 138 kDa) and to tryptic fragments of this pump. Antibody JA3, previously used for staining of human kidney tubules, reacts with a different set of tryptic fragments, showing that the two antibodies are directed against different regions or conformational determinants on the pump molecule. We show that Ca2+-Mg2+-ATPase and 28-kDa CaBP are present in the principal cells of the distal convoluted tubule of the rat and are absent in intercalated cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

[The effect of stimulation of the beta-adrenoreceptors on ion and water transport in the distal kidney tubule of the triton].

The ion and fluid reabsorption during perfusion of inter-tubular capillaries with different subtypes of beta-adrenergic agonists was studied in the newt distal tubule using the micropuncture technique and X-ray microanalysis. Isoproterenol (10(-5) M) did not affect the ion and water transport. Stimulation of beta 1-adrenergic receptor with isoproterenol and beta 2-adrenergic antagonist ICI 118.551 inhibited the fractional reabsorption of sodium, chloride and magnesium, the fluid reabsorption being changed insignificantly. Stimulation of beta 2-adrenergic receptor with ventolin increased the fractional calcium reabsorption. The transport of water and other ions did not change.

Adrenergic beta-Antagonists↗
PubMed2000

Calcitriol upregulates expression and activity of the 1b isoform of the plasma membrane calcium pump in immortalized distal kidney tubular cells.

The plasma membrane calcium pump (PMCA) is ubiquitously expressed in calcium transporting epithelia. PMCA is encoded by four distinct genes (PMCA1-4) which can be further posttranscriptionally modified. PMCA1b is the only isoform of PMCA1 expressed in kidney and intestine. Calcitriol upregulates PMCA protein expression and activity and PMCA1 mRNA expression in the intestine. Calcitriol has a similar effect on kidney distal tubule PMCA activity in vivo but the cellular basis for this effect has not been studied. PMCA expression in Madin-Darby bovine kidney (MDBK) cells, a distal kidney tubule cell line, was compared with a proximal tubule (LLC-PK1) and embryonic (HEK 293) kidney cell line. Only MDBK cells express PMCA1b mRNA and PMCA protein. In MDBK cells, calcitriol increased steady state expression of PMCA1b mRNA and protein and upregulated the functional activity of PMCA on calcium transport to a similar degree. Furthermore, calcitriol enhanced PMCA1b mRNA stability. These data are consistent with in vivo localization studies demonstrating the distal kidney tubule localization of PMCA protein. Furthermore, they indicate that calcitriol is an important regulator of PMCA activity in the kidney distal tubule by a pathway that includes translation and posttranscriptional modification of PMCA1b.

Animals↗
PubMed2006

Differential regulation of B/K protein expression in proximal and distal tubules of rat kidneys with ischemia-reperfusion injury.

Brain/kidney (B/K) protein is a novel double C2-like-domain protein that is highly expressed in rat brain and kidney, but its cellular localization and functional role in the kidney are still undetermined. We examined the cellular localization of B/K protein in the rat kidney under normal and ischemic conditions. Ischemia-reperfusion (I/R) injury was induced by clamping both renal arteries for 45 min, and animals were killed at 1 and 6 h and 1, 2, 3, 5, 7, 14, and 28 days after the reperfusion. Kidney tissues were processed for immunohistochemistry and immunoblot analyses using rabbit anti-B/K polyclonal antibodies. In control kidneys, B/K protein was expressed primarily in distal tubules including the thick ascending limb, distal convoluted and connecting tubules, and collecting duct. Notably, B/K protein was also expressed in the straight portion (S3 segment), but not in the S1 or S2, of proximal tubules, and podocytes of the glomerulus. In rat kidneys with I/R injury, expression of B/K protein was differentially regulated according to the anatomic location. In distal tubules, overall expression of B/K protein was markedly decreased. On the other hand, I/R injury significantly increased B/K protein expression in the S3 segment of the outer medulla as well as in the rat proximal tubular epithelial cell line NRK-52E in vitro. Furthermore, B/K protein was strongly expressed in many exfoliated cells in the lumen and urine. These findings suggest that B/K protein is closely associated with cell death in proximal tubules, which are vulnerable to I/R injury in the kidney.

Animals↗
PubMed1998

In vivo dose-related receptor binding of the vitamin D analogue [3H]-1,25-dihydroxy-22-oxavitamin D3 (OCT) in rat parathyroid, kidney distal and proximal tubules, duodenum, and skin, studied by quantitative receptor autoradiography.

1,25-Dihydroxy-22-oxavitamin D3 (OCT) is a new synthetic analogue of 1,25(OH)2D3 with a low calcemic effect. This study utilized quantitative receptor autoradiography to determine the dose-related receptor binding and saturation among the vitamin D target cells: parathyroid chief cells, kidney distal and proximal tubule epithelium, duodenal absorptive epithelium, and epidermal keratinocytes. Rats were injected with 0.25, 0.5, 1.0, 2.0, 4.0, 8.0, or 16.0 microgram/kg bw of [26-3H]-OCT and sacrificed 1 hr afterwards. Then autoradiographs were prepared under identical conditions. In these target cells, nuclear uptake of radioactivity increased with dose and then achieved a plateau. However, their saturation doses showed differences: parathyroid chief cells 1-2 microgram duodenal absorptive epithelium, distal tubule epithelium, and epidermal keratinocytes 4-6 microgram proximal tubule epithelium 8 microgram (per kg bw). In contrast, in nontarget cells, such as liver and duodenal smooth muscle, radioactivity did not concentrate in the nuclei but increased in the cytoplasm with dose, without plateauing. These results provide the first information on the relative saturabilities of various target cell populations with a vitamin D ligand. Parathyroid chief cells required the relatively lowest receptor saturation dose. This suggests a high sensitivity and response to OCT treatment with related therapeutic potential for the regulation of parathyroid function.

Animals↗
PubMed1977

Homogeneous cell populations from rabbit kidney cortex. Proximal, distal tubule, and renin-active cell isolated by free-flow electrophoresis.

A single-cell suspension has been prepared from rabbit kidney cortex by using a Ca-binding medium and gentle mechanical forces. The suspension was subjected to carrier-free electrophoresis, and several cell fractions were obtained. Proximal and distal tubule cell populations could be identified by their morphology. Renin-containing cells were located by means of radioimmunoassay. The morphology of the cells and their vitality (uridine incorporation) are discussed.

Animals↗