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Query: UNIPROT:P41181 (collecting duct)
 5,183 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

It is widely accepted that in vivo the function of the papilla of the mammalian kidney is supported primarily by anaerobic metabolism. As a result, the major source of energy for support of function in the papilla is considered to be derived from glycolysis. This orientation originates from two concepts: 1) that in vivo the gaseous environment of the papilla has such a low PO2 that O2 availability limits O2 consumption, and 2) that papillary tissue has a high rate of glycolysis when compared with either cortical tissue or extrarenal tissues. It has also been tacitly assumed that papillary tissue has a "low" O2 uptake. Review of the measurements of PO2 of papillary tissue and of urine PO2 indicates that the PO2 of papillary tissue should not limit its aerobic mitochondrial oxidative metabolism. While the rate of aerobic glycolysis in papillary tissue is high, simultaneously papillary tissue has a rate of O2 uptake similar to that of liver and higher than that of muscle. The major (two-thirds) source of energy for papillary tissue in vitro is from O2 uptake. That papillary tissue is not exclusively dependent on glucose for its energy requirements is indicated by the greater stimulation of papillary tissue QO2 by succinate than by glucose. Thus, papillary tissue has both a high aerobic mitochondrial oxidative metabolism and a high aerobic glycolytic metabolism. It is suggested that the mechanism for the high rate of aerobic glycolysis in the presence of an adequate O2 supply is due to the relatively small mass of mitochondria in papillary tissue in relation to the amount of work done by the tissue. As a result of the limited rate of ATP production by the mitochondrial electron transport chain, the phosphorylation state ([ATP]/[ADP][Pi]) is reduced and the cytoplasmic redox state ([NAD+]/[NADH]) of the papillary collecting duct cells also becomes more reduced; changes in both ratios enhance the rate of glycolysis. This limited metabolic capacity of the collecting duct cells may permit an excess volume of solute and water to be excreted during volume expansion diuresis. The metabolic characteristics of the papilla, when compared to cortex, also provide a basis for the observed differences in substrate selectivity of cortex and medulla with respect to utilization of glucose and lactate. The experimental approaches that may provide information bearing on the suggested mechanisms for regulation of papillary metabolism in relation to tubular work functions are indicated.
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PMID:Is the function of the renal papilla coupled exclusively to an anaerobic pattern of metabolism? 22 Aug 81

We used the patch-clamp technique to study the effects of ATP on the small-conductance potassium channel in the apical membrane of rat cortical collecting duct (CCD). This channel has a high open probability (0.96) in the cell-attached mode but activity frequently disappeared progressively within 1-10 min after channel excision (channel "run-down"). Two effects of ATP were observed. Using inside-out patches, low concentrations of ATP (0.05-0.1 mM) restored channel activity in the presence of cAMP-dependent protein kinase A (PKA). In contrast, high concentrations (1 mM) of adenosine triphosphate (ATP) reduced the open probability (Po) of the channel in inside-out patches from 0.96 to 0. 1.2 mM adenosine diphosphate (ADP) also blocked channel activity completely, but 2 mM adenosine 5'-[beta,gamma-imido]triphosphate (AMP-PNP), a nonhydrolyzable ATP analogue, reduced Po only from 0.96 to 0.87. The half-maximal inhibition (Ki) of ATP and ADP was 0.5 and 0.6 mM, respectively, and the Hill coefficient of both ATP and ADP was close to 3. Addition of 0.2 or 0.4 mM ADP shifted the Ki of ATP to 1.0 and 2.0 mM, respectively. ADP did not alter the Hill coefficient. Reduction of the bath pH from 7.4 to 7.2 reduced the Ki of ATP to 0.3 mM. In contrast, a decrease of the free Mg2+ concentration from 1.6 mM to 20 microM increased the Ki of ATP to 1.6 mM without changing the Hill coefficient; ADP was still able to relieve the ATP-induced inhibition of channel activity over this low range of free Mg2+ concentrations. The blocking effect of ATP on channel activity in inside-out patches could be attenuated by adding exogenous PKA catalytic subunit to the bath. The dual effects of ATP on the potassium channel can be explained by assuming that (a) ATP is a substrate for PKA that phosphorylates the potassium channel to maintain normal function. (b) High concentrations of ATP inhibit the channel activity; we propose that the ATP-induced blockade results from inhibition of PKA-induced channel phosphorylation.
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PMID:Dual effect of adenosine triphosphate on the apical small conductance K+ channel of the rat cortical collecting duct. 194 Aug 49

A plasma membrane ATPase sensitive to inhibition by N-ethylmaleimide (NEM) and insensitive to inhibition by oligomycin and ouabain has been shown to be involved in acidification of urine in the turtle bladder. The activity of this NEM-sensitive ATPase was determined in four types of distal nephron segments of normal rats and in rats treated with ammonium chloride. The enzyme activity was determined by a fluorometric micromethod in which ATP hydrolysis was coupled to NADH oxidation. Significant activities (10-35 pmol ADP X min-1 X mm-1) of NEM-sensitive ATPase were present in the distal convoluted tubule (DCT) and in the cortical and outer and inner medullary collecting duct segments of normal rats. In metabolic acidosis produced by ammonium chloride treatment (plasma CO2 content = 15.3 +/- 0.8 mequiv./L), the NEM-sensitive ATPase activity was increased significantly (60-100%) in the collecting duct segments without showing a significant change in the enzyme activity in the DCT. Our data are consistent with the hypothesis that a plasma membrane H+-ATPase (inhibited by NEM but not by oligomycin or ouabain) is involved in H+ secretion in the mammalian collecting duct.
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PMID:Stimulation of an N-ethylmaleimide-sensitive ATPase in the collecting duct segments of the rat nephron by metabolic acidosis. 293 19

Mineralocorticoids play a major role in the regulation of sodium transport in a variety of tissues, including the cortical collecting duct (CCD) of the mammalian nephron. To assess, in part, the underlying mechanism(s) of this control, the present studies were designed to evaluate, first, the influence of mineralocorticoids on the Na-K-ATPase activity in the rabbit CCD and, secondly, a possible role of sodium entry into the cell at the luminal border on the regulation of the Na-K-ATPase. In the first series of studies, rabbits were maintained on a low sodium diet which raised serum aldosterone levels from 16 to 70 ng/dl after 3-4 days, with further elevations being expressed with treatment for two weeks or more. In CCDs isolated from these animals, the Na-K-ATPase increased from 13 to 40 pmol ADP min-1 mm-1 after 3-4 days on the low sodium regimen, but then declined, returning to control values after approximately 2 weeks. This decline in activity was preceded by a decrease in the Na+ concentration of the urine to low levels and hence, likely coincided with a decreased delivery of sodium to, and sodium entry into the cells of, the CCD. If dietary manipulations were used to maintain a high delivery of sodium to the CCD in the animal, elevation of plasma mineralocorticoid levels by treatment with deoxycorticosterone acetate (DOCA) caused a similar elevation in the Na-K-ATPase activity after 3-4 days, which did not decline with continued treatment for up to 2 weeks. Furthermore, it was observed that mineralocorticoids only exerted their effect on the Na-K-ATPase after a latent period of 1 day, well after sodium excretion had fallen, indicating that sodium entry into the CCD cells was already stimulated. If animals were simultaneously treated with DOCA and the sodium channel blocker amiloride for 3-4 days, the effects on the Na-K-ATPase were markedly reduced, whereas amiloride treatment alone had no effect on the enzyme activity. Since others have shown that mineralocorticoids induce synthesis of the Na-K-ATPase subunits in toad bladder cells in an amiloride-insensitive manner, sodium must be exerting its effect on a process after translation. It is concluded that the initial effect of mineralocorticoids in the CCD is on sodium entry with a delayed induction of the Na-K-ATPase, which is regulated by Na-dependent modulation of a posttranslational process.
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PMID:Sodium-dependent modulation of the renal Na-K-ATPase: influence of mineralocorticoids on the cortical collecting duct. 298 28

Rat renal papillary collecting duct (PCD) cells were isolated using collagenase and hyaluronidase digestion and a three-step low-speed centrifugation. As assessed by binding of the lectin Dolichos biflorus and determination of vasopressin-sensitive adenylate cyclase and Na+-K+-ATPase, the enrichment of PCD cells over a crude papillary cell preparation was 1.8, 2.4, and 1.4, respectively. Microscopic evaluation indicated that the preparation was greater than 90% pure PCD cells. The isolated cells were viable as evident from the high K/Na ratio of intracellular electrolytes measured by electron probe analysis (5.3), from the high ATP/ADP ratio (2.15), and the metabolic response to alterations in Na transport. Exposure to 2 mM ouabain or removal of Na reduced O2 consumption by 25-35%; the uncoupler carboxylcyanide-m-chlorophenylhydrazone more than doubled O2 consumption. In the presence of 14 mM glucose and at a PO2 of 100 Torr the cells produced substantial quantities of lactate. This aerobic glycolysis may account for greater than 20% of the ATP production. In the presence of rotenone, glycolysis increased by 56% and was able to maintain the cellular ATP level at 65% of control. In the absence of any exogenous substrate PCD cells respired normally and had a close to normal ATP content, but lactate production was markedly decreased. These results demonstrate that viable PCD cells can be isolated from rat kidney. At normal PO2 and in the presence of D-glucose the cells show a substantial amount of aerobic glycolysis, although their mitochondrial respiration is not rate limiting. In the absence of glucose the cells derive the majority of their energy from an as yet unidentified endogenous substrate.
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PMID:Purification of rat papillary collecting duct cells: functional and metabolic assessment. 330 74

The ATPase activity of rabbit isolated renal tubule segments was measured using a microtechnique in which the hydrolysis of ATP was enzymatically coupled to the appearance of an alkali-converted, highly fluorescent form of nicotinamide adenine dinucleotide. The methods are simple, reproducible, and have a high sensitivity in which picomole quantities of hydrolyzed ATP can readily be measured. Several methods for permeabilizing the cell membranes for measurement of Na+-K+-ATPase activity were evaluated, including osmotic (distilled water or 300 mM imidazole) and temperature (freezing) shock and addition of the nonionic detergent octylglucoside. An octylglucoside concentration of 0.5% was found to cause a maximum activation of the Na+-K+-ATPase and was comparable with that observed when tubules were permeabilized by exposure to distilled water and freezing. Incubation of tubules in 300 mM imidazole was less effective in permeabilizing the cell membranes. In all subsequent studies, the cells were permeabilized by exposure to distilled water and freezing as done by others. The methods were used to assay for the basal levels of Na+-K+-ATPase in the superficial proximal convoluted tubule, the superficial proximal straight tubule, and the cortical collecting tubule and were found to average 44.9 +/- 6.3, 26.4 +/- 2.4, and 11.8 +/- 2.2 pmol ADP X mm-1 X min-1, respectively. Furthermore, elevation of plasma mineralocorticoids by daily injections of deoxycorticosterone acetate (2 mg X kg-1 X day-1) for 4-15 days caused a doubling in the Na+-K+-ATPase activity of the cortical collecting duct, confirming the results of others. The methods presented can easily be adapted for microanalysis of other ATPases.
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PMID:Micromethodology for measuring ATPase activity in renal tubules: mineralocorticoid influence. 609 64

A new method of isolating human eccrine sweat glands by the repeated dissection of skin biopsies with scissors is described. The success of the technique is attributed to a potential line of weakness between the investing capsule and the surrounding connective tissue, which parts under shear forces. The yield is 20-50 glands per biopsy (5 cm X 0.5 cm). The glands are judged to be viable by: (i) light and electron microscopy; (ii) ATP, ADP and AMP contents of 81.0 +/- 12.7, 13.8 +/- 3.3 and 3.8 +/- 1.0 pmol/gland, respectively (mean +/- S.E.M.), which gave an energy charge of 0.90; (iii) the 28-fold rise in cyclic GMP content and the sevenfold rise in cyclic AMP content effected by treatment for 2 min with 10(-5) M-acetylcholine and for 10 min with 10(-5) M-isoprenaline, respectively; (iv) the rate of [3H]leucine uptake into protein; and (v) the concentration of Neutral Red by the collecting duct. Glands were maintained for 7 days on polycarbonate filters floating on RPMI 1640 tissue-culture medium. After this time the ATP, ADP and AMP contents were 63.2 +/- 7.3, 8.5 +/- 2.2 and 3.5 +/- 0.8 pmol/gland, respectively (mean +/- S.E.M.), which gave an energy charge of 0.90. During maintenance a dilatation of the intercellular spaces developed in both secretory coil and collecting duct. Following maintenance there was a significant rise in the rate of [3H]leucine uptake into protein. Maintained glands demonstrated a fivefold greater accumulation of cyclic AMP in response to isoprenaline than did freshly isolated glands, but there was no comparable maintenance hypersensitivity of cyclic GMP to acetylcholine. This pattern of adrenergic, but not cholinergic, maintenance hypersensitivity matches the known lack of denervation hypersensitivity of human eccrine sweat glands to acetylcholine in vivo.
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PMID:Biochemical and ultrastructural studies of human eccrine sweat glands isolated by shearing and maintained for seven days. 609 35

Na-K-ATPase activity was determined in 10 segments of the rat nephron using a fluorometric microassay method [4]. The enzyme activity showed three peaks (greater than 200 pmol ADP min-1 mm-1) along the nephron of normal rats. These peaks were in the S1 portion of the proximal tubule, the medullary thick ascending limb from the inner stripe and the distal convoluted tubule. Feeding the rats a low potassium diet for 8 weeks produced a significant decrease in Na-K-ATPase activity in the cortical collecting duct, but no significant change in this enzyme in any other segment. The low potassium diet did not produce a significant change in Mg-ATPase in any nephron segments. We conclude that Na-K-ATPase activity along the rat nephron shows a pattern that is qualitatively similar to that seen in the rabbit nephron [4]. However, quantitatively the Na-K-ATPase activity in the rat nephron is greater than in the corresponding segments of the rabbit nephron. The results are consistent with the greater rate of glomerular filtration and Na+ reabsorption per rat nephron. Furthermore, our results suggest that the decrease in potassium excretion during potassium deficiency is modulated, at least in part, by the level of Na-K-ATPase activity in the cortical collecting duct.
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PMID:Effect of low potassium-diet on Na-K-ATPase in rat nephron segments. 628 58

The renal collecting duct is a major target for the mineralocorticoid hormone aldosterone which acts to enhance electrogenic Na+ absorption. The cortical portion of the collecting duct displays a vigorous response to mineralocorticoids administered in vivo. The terminal, or inner medullary portion, does not usually display such a vigorous response; the reason for this difference is unknown. To explore one possible mechanism for this lack of response, we varied the conditions of culturing these cells and determined that serum inhibited the ability of aldosterone to enhance Na+ transport. By screening 11 peptides, we found that transforming growth factor (TGF)-beta 1 produced a concentration-dependent inhibition of the action of aldosterone. The action of TGF-beta 1 required at least several hours of incubation. Resistance to the action of aldosterone could be produced by preincubating the monolayers with TGF-beta 1 for a few hours; subsequent exposure to aldosterone for up to 48 h failed to stimulate Na+ transport. TGF-beta 1 did not produce a change in cell morphology or the content of DNA, ATP, or ADP; there was a small reduction in protein content. Pretreatment with cycloheximide failed to reproduce the TGF-beta 1 effect. The induction of resistance to mineralocorticoid hormone may play an important role in modulating the effects of aldosterone on Na+ homeostasis.
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PMID:Induction of resistance to mineralocorticoid hormone in cultured inner medullary collecting duct cells by TGF-beta 1. 752 8

Ion channels in the apical membrane of rat inner medullary collecting duct (IMCD) were investigated by the patch clamp technique. Owing to the histological heterogeneity of IMCD, cells were cultured from the lower half of the inner medulla of Wistar rat kidney. Channel activity was rarely seen in cell attached patch, but membrane excision activated multiple units of 28.2 +/- 0.7 pS cation selective channel. A Na or K selective channel was not found. The 28 pS channel showed membrane voltage dependency, no rectification, almost equal permeability to monovalent cations (Na/K/Li/Cs/Rb/NH4 = 1:1.00:0.82:0.97:1.10:1.71) and no significant permeation to anions or divalent cations. Calcium of the cytoplasmic side from 10(-7) M to 10(-4) M affected the mean number of open channels (nPo) dose-dependently in excised patch (IC50 = 5 x 10(-6) M). 1 mM of ATP, ADP, AMP and gadolinium reversibly suppressed nPo to near zero whereas amiloride, cAMP or cGMP had no effect. Multiple conductance substates were frequently observed. These results suggested that this channel belongs to the nonselective cation channels which has been identified in other epithelia and is not responsible for amiloride sensitive Na transport through IMCD cells.
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PMID:Monovalent cation selective channel in the apical membrane of rat inner medullary collecting duct cells in primary culture. 753 35


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