Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cultured inner medullary collecting duct (IMCD) cells have been shown to secrete protons (H+) by two mechanisms: an N-ethylmaleimide- and dicyclohexyl-carbodiimide-sensitive electrogenic H(+)-ATPase or H+ pump, and an amiloride-sensitive, secondary active Na+H+ exchanger. These cells also express Cl-/HCO3- exchange and carbonic anhydrase activity in common with other renal epithelial cells involved in acid-base transport. Video fluorescence microscopy of individual cells using 2',7'-biscarboxyethyl-5(6)-carboxyfluorescein has demonstrated that adjacent-cultured IMCD cells show substantial functional intercellular heterogeneity. The development of H(+)-pumping activity is associated with high-baseline intracellular pH and peanut agglutinin (PNA) affinity, and loss of mitotic activity and of Na+/H+ exchange. The H(+)-pumping activity may be further enhanced by removal of fetal calf serum for 6-54 h or by selecting cells with high PNA affinity. IMCD cells in their most differentiated state form domes, which consistently showed the highest rates of H(+)-pumping activity, as well as high affinity for peanut lectin. When IMCD were plated at low density, domes developed relatively late (2-4 weeks), at which time cells located in the center of nests of contiguously growing cells were quiescent and showed H(+)-pumping activity but no Na+/H+ exchange. On the other hand, dense plating was associated with early development of domes (end of 1st week), at which time adjacent cells showed a high mitotic activity and Na+/H+ exchange, but no H(+)-pumping activity. We speculate that differentiation of IMCD cells results in the development of cell polarity.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Differentiation of proton-pumping activity in cultured renal inner medullary collecting duct cells. 216 49

To examine mechanisms of H+ extrusion in the inner stripe of outer medullary collecting duct (OMCDIS), cell pH (pHi) was measured microfluorometrically in in vitro perfused tubules by use of 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. In total absence of luminal and peritubular Na+, pHi recovery from an acid load (NH3/NH+4 pulse) occurred at an initial rate of 0.13 +/- 0.02 pH units/min, whereas in the presence of 135 mM peritubular Na+, pHi recovered at 1.40 +/- 0.28 pH units/min. Na(+)-dependent pHi recovery was completely inhibited by 1.0 mM peritubular amiloride. Luminal Na+ (135 mM) addition had no effect on pHi recovery. Na(+)-independent pHi recovery from acid load was manifest by a triphasic response: 1) initial slow alkalinization; 2) slow cell acidification; and 3) a final phase that exhibited gradually increasing rates of alkalinization, returning pHi above the initial control level (pre-NH3/NH+4 pulse). Luminal N-ethylmaleimide (NEM, 500 microM), an H(+)-ATPase inhibitor, significantly inhibited initial rate of pHi recovery and total pHi recovery; whereas 500 microM peritubular NEM had no effect on initial rate of pHi recovery. Luminal SCH 28080 (100 microM), an H(+)-K(+)-ATPase inhibitor, had no effect on initial rate of pHi recovery or total pHi recovery. Thus rabbit OMCDIS possesses both an apical membrane NEM-sensitive, SCH 28080-insensitive, Na(+)-independent H+ extrusion mechanism (likely a simple H(+)-translocating ATPase) and a basolateral membrane amiloride-sensitive Na(+)-H+ antiporter.
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PMID:Apical and basolateral membrane H+ extrusion mechanisms in inner stripe of rabbit outer medullary collecting duct. 217 59

Biochemical and physiologic studies in individual segments of the cortical collecting duct (CCD) and outer medullary collecting duct (OMCD) have provided evidence for the presence of an H-K-ATPase which is involved in the reabsorption of potassium in exchange for protons. The present study was designed to determine the cellular distribution of H-K-ATPase immunoreactivity in the CCD and OMCD of the rat and rabbit using mouse monoclonal antibodies against hog gastric H-K-ATPase. Kidneys of normal rats and rabbits were preserved for light microscopic immunohistochemistry and embedded in paraffin. Sections were incubated with the primary antibody followed by the avidin-biotin-horseradish peroxidase procedure. Sections incubated without primary antibody or with a non-specific mouse Ig served as controls. Light microscopy revealed diffuse cytoplasmic staining indicating H-K-ATPase immunoreactivity in intercalated cells in the CCD and OMCD in both rat and rabbit. In all segments studied except the rat CCD, the percentage of H-K-ATPase immunoreactive cells corresponded to the percentage of intercalated cells. In the rat CCD only 23% of the cells were reactive with H-K-ATPase antibodies, which is less than the percentage of intercalated cells in this region. It is possible that only type A intercalated cells possess H-K-ATPase immunoreactivity or that some intercalated cells did not have sufficient activity to be detected by our method. These results demonstrate H-K-ATPase immunoreactivity in the intercalated cells of the CCD and OMCD of rat and rabbit, suggesting that these cells are involved in potassium reabsorption in exchange for proton secretion in the mammalian collecting duct.
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PMID:H-K-ATPase immunoreactivity in cortical and outer medullary collecting duct. 217 57

Li+ is actively transported out of cells, and across different epithelia of both mammalian and amphibian origin. Due to the low affinity of the Na+/K(+)-ATPase for Li+, the transport is most likely energized by exchange and/or cotransport processes. The detailed mechanism by which Li+ is reabsorbed across the proximal tubule is not known, although it seems reasonable to assume that at least a part is by secondary active transcellular transport. The evidence further suggest that aldosterone and maybe vasopressin, through their effects on the Na+ channels in the late distal tubule and the collecting duct may be of significance in inducing distal Li+ reabsorption, as seen during severe sodium restriction in rats and dogs. Clearly more studies are needed to finally resolve these issues.
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PMID:Lithium transport across biological membranes. 218 30

Significant proximal tubular responses to exogenous dopamine require 0.1 to 10 mumol/L concentrations but endogenous peritubular dopamine and DOPA concentrations are in the picomolar to nanomolar range. Dopamine concentration approaches micromolar levels within proximal tubular cells and their brush borders, as a result of DOPA decarboxylation and secretion, and in collecting duct fluid, as a result of tubular fluid absorption. Thus dopamine probably acts either within the proximal tubule cell or brush border or from the collecting tubular lumen. DOPA and Na+ uptake are coupled; dopamine uptake is linked to intracellular electrical potential and its secretion to H+ counter-transport; therefore alterations in proximal tubular Na+ and H+ transport influence dopamine excretion. Haloperidol and SCH 23390 block dopamine excretion, therefore dopamine antagonists may inhibit tubular dopamine responses by lowering intracellular dopamine concentration as well as by receptor blockade. Evidence for an intracellular site of dopamine action can be deduced from the inhibitory effect of DOPA on oxygen consumption and 86Rb uptake in proximal tubule cells. We have confirmed these findings in isolated proximal tubule cells but not in proximal tubule fragments. The discrepant responses may be due to the fact that isolated cells loose their polarity while tubule fragments remain polarized. Dopamine inhibition of proximal tubular Na+, K(+)-ATPase is not reproduced by single dopamine agonists or inhibited by dopamine antagonists. Dopamine effects which are not linked to known dopamine receptors may be the result of redox cycling. Micromolar dopamine oxidizes sulfhydryl groups which may modify enzyme structure and activate protein kinase C.
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PMID:Functional effects of proximal tubular dopamine production. 220 Apr 36

To investigate the direct epithelial effects of corticosteroids on renal ion transport, we studied the influence of the pure glucocorticoid agonist RU 28362 and aldosterone on Na+ and K+ transport in primary cultures of immunodissected rabbit cortical collecting duct (CCD) cells. When grown on permeable supports in a steroid-free medium, CCD monolayers exhibited a lumen-negative transepithelial potential difference (PD) of 5.2 +/- 1.07 mV and a short-circuit current (SCC) of 8.54 +/- 2.2 microA/cm2. Transepithelial resistance averaged 660 +/- 49 omega/cm2. The cultures actively reabsorbed Na+ and secreted K+. Both aldosterone and RU 28362 significantly increased PD and SCC; the effects were time and dose dependent. The effect of RU 28362 was completely prevented by the glucocorticoid receptor antagonist RU 486, whereas ZK 91587, a specific mineralocorticoid receptor antagonist, did not block its effect. Both aldosterone and RU 28362 increased the bath-to-lumen concentration ratio of Na+ while lowering that of K+, indicating an increased Na+ reabsorption and K+ secretion. The number of Na(+)-K(+)-ATPase units was significantly enhanced (approximately 2-fold) by both RU 28362 and aldosterone. These results demonstrate that, in cultured CCD cells, not only aldosterone but also a pure glucocorticoid is able to exert mineralocorticoid-like effects, and this latter effect is mediated by glucocorticoid receptors. Because all parameters studied responded similarly to aldosterone and RU 28362, we speculate that in CCD cells glucocorticoids and mineralocorticoids might act by regulating the same gene(s).
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PMID:Glucocorticoid receptors mediate mineralocorticoid-like effects in cultured collecting duct cells. 222 Nov 5

Stimulation or inhibition of H+ secretion has been associated with characteristic ultrastructural changes in various epithelial cells, including the parietal cell of the gastric mucosa, the carbonic anhydrase (CA)-rich cell of the turtle urinary bladder, and the intercalated (I) cell of the mammalian collecting duct. An electroneutral potassium-activated H+-ATPase is responsible for H+ secretion in the stomach, whereas acidification in the turtle bladder and the mammalian collecting duct is mediated by an electrogenic H+-translocating ATPase. Despite these differences, the parietal cell, the CA-rich cell, and the I cell have several morphological features in common. They are rich in mitochondria, contain numerous tubulovesicular membrane structures in the apical region of the cell, and possess a variable number of microprojections on the luminal surface. After stimulation of H+ secretion there is a significant increase in the surface area of the apical membrane concomitant with a decrease in the tubulovesicular membrane compartment in these cells, as revealed by morphometric analysis. These findings suggest that membrane (possibly containing an H+ pump) is being transferred from the tubulovesicular compartment to the apical plasma membrane on stimulation of H+ secretion. A hypothesis of membrane recycling is proposed to account for the observed morphological changes.
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PMID:Structure-function relationships in H+-secreting epithelia. 241 Feb 97

Proton secretion in the renal medullary collecting duct is thought to occur via a luminal proton-ATPase. In order to determine what mechanism(s) participate in proton transport across medullary collecting duct (MCD) cells membranes, intracellular pH (pHi) regulation and proton extrusion rates were measured in freshly prepared suspensions of rabbit outer MCD cells. Cells were separated by protease digestion and purified by Ficoll gradient centrifugation. pHi was estimated fluorometrically using the entrapped intracytoplasmic pH indicator, 6-carboxyfluorescein. Proton extrusion rates were measured using a pH stat. The resting pHi of MCD cells was 7.19 +/- 0.05 (SE) in a nonbicarbonate medium of pH 7.30. When cells were acidified by exposure to acetate salts or by abrupt withdrawal of ammonium chloride, they exhibited pHi recovery to the resting pHi over a 5-min time-course. Depletion of greater than 95% of cellular ATP content by poisoning with KCN in the absence of glucose inhibited pHi recovery. ATP depletion inhibited proton extrusion from MCD cells. Treatment with N-ethylmaleimide also inhibited pHi recovery. In addition, cellular ATP content was dependent on transmembrane pH gradients, suggesting that proton extrusion stimulated ATP hydrolysis. Neither removal of extracellular sodium nor addition of amiloride inhibited pHi recovery. These results provide direct evidence that a plasma membrane proton-ATPase, but not a Na+/H+ exchanger, plays a role in proton transport and pHi regulation in rabbit MCD.
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PMID:Intracellular pH regulation and proton transport by rabbit renal medullary collecting duct cells. Role of plasma membrane proton adenosine triphosphatase. 241 58

Immunocytochemical detection of carbonic anhydrase (CA II), (Na+-K+)-ATPase and the anion channel (band 3) glycoprotein was used to study structural and functional heterogeneity of cells lining the collecting ducts, especially of intercalated cells, in the rat kidney. High content of CA II was found in intercalated cells as determined by morphology, although a weak diffuse cytoplasmic staining of this enzyme could be observed also in a subpopulation of principal cells. (Na+-K+)-ATPase could be detected exclusively in principal cells, whereas basolateral band 3 immunoreactivity was seen only in a subpopulation of intercalated cells. Double immunostaining experiments revealed that the weak cytoplasmic type of CA II and basolateral (Na+-K+)-ATPase immunoreactivities were colocalized in 20 to 30% (depending on the segment studied) of the collecting duct epithelial cells but, in contrast, cells rich in CA II or those with basal band 3 immunoreactivity seldom contained (Na+-K+)-ATPase. Instead, band 3 glycoprotein and the abundant CA II were colocalized in 20 to 35% of the cells in various segments of collecting ducts, whereas, band 3 and weak cytoplasmic CA II were seldom seen in the same cells. The results show that the current approach is useful for identifying and characterizing two distinct subpopulations of intercalated cells, both rich in CA II but differing in respect to the presence or absence of band 3 glycoprotein. On the basis of physiologic and biochemical data of the functions of these transport proteins we propose that the subpopulations of intercalated cells thus identified represent the acidifying and alkalinizing subtypes, respectively.
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PMID:Immunocytochemical characterization of carbonic anhydrase-rich cells in the rat kidney collecting duct. 244 Nov 37

Amiloride, triamterene, and the spirolactones are potassium-sparing diuretics which act on the distal parts of the nephron, from the late distal tubule to the collecting duct. In these segments, active sodium reabsorption occurs through the following mechanism: sodium ions enter the cell through specific channels present in the luminal membrane and are extruded out of the cell into the peritubular medium by a sodium-potassium exchange pump, the Na-K-ATPase. Amiloride in micromolar concentrations reduces the sodium transport by blocking the luminal membrane sodium channel. Triamterene has a similar effect, although with a lower affinity; the available studies do not allow to determine if an inhibitory effect of triamterene on the Na-K-ATPase plays an additional role in its diuretic action. The spirolactones are competitive inhibitors of aldosterone, the mineralocorticoid hormone which promotes sodium reabsorption by increasing both the number of active sodium channels in the luminal membrane and the number of active Na-K pumps in the peritubular membrane. By the inhibitory effect on the electrogenic sodium transport, amiloride, triamterene, and the spirolactones decrease the lumen-negative transepithelial potential difference. This reduces the driving force for potassium movement into the tubular lumen and thus decreases potassium excretion.
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PMID:Potassium-sparing diuretics. 245 8


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