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At least 631 records · Page 35Linked to original sources
PubMed1987

Ultrastructural localization of adenosine triphosphatase activity in HeLa cells at various stages of the cell cycle.

HeLa cells in a monolayer culture were synchronized to S, G2 and mitotic phases by use of excess (2.5 mM) deoxythymidine double-block technique. The localizations of Ca2++-activated adenosine triphosphatase (ATPase) at different phases of the cell cycle were studied using light- and electron-microscopic histochemical techniques, and microphotometric comparisons of the densities of reaction products. Enzyme reaction product was always localized in the endoplasmic reticulum, nuclear membrane, mitochondria and Golgi apparatus, but there were qualitative and quantitative differences related to the phases of the cell cycle. In S phase the activity was mainly concentrated in a perinuclear area of the cytoplasm whereas in G2 and mitosis the activity was scattered throughout the cell. The total activity per cell was maximal in G2, was less in S phase and least in mitosis. Activity in the mitochondria and endoplasmic reticulum was distinctly less in mitosis than in other phases of the cell cycle. The mitochondrial ATPase differed from the ATPase at other sites in ion dependence and sensitivity to oligomycin. The results suggest that there may be several distinct ATPases in proliferating cells.

Adenosine Triphosphatases↗
PubMed1978

Assembly of the sarcoplasmic reticulum. Synthesis of calsequestrin and the Ca2+ + Mg2+ -adenosine triphosphatase on membrane-bound polyribosomes.

Membrane-bound and free polyribosomes were isolated from skeletal muscle of neonatal rats and messages were translated in a rabbit reticulocyte lysate treated with Ca2+ -dependent nuclease to reduce endogenous messenger translation. Newly synthesized calsequestrin and adenosine triphosphatase (ATPase) sere isolated by antibody precipitation, followed by separation of the precipitates in SDS-polyacrylamide gels. Radioactivity in calsequestrin and the ATPase were counted in gel slices. Calsewuestrin and the ATPase were both found to be synthesized on membrane-bound polyribosomes. Since calsequestrin is a glycoprotein, localized in Golgi regions in early stages of muscle cell differentiation, it is probable that its synthesis follows the pathway for synthesis of secreted proteins except that its destination is the luminal space of a cellular organelle. The disposition of the ATPase during synthesis is, as yet, unknown.

Adenosine Triphosphatases↗
PubMed2006

Vacuolar adenosine triphosphatase and pancreatic acinar cell function.

The pathologic activation of proteases within the pancreatic acinar cell is a key initiating event in acute pancreatitis. Past studies have suggested that the generation of a low-pH environment is critical to this process. Vacuolar adenosine triphosphatase (vATPase) is a multiprotein complex that transports protons across cellular membranes. Activation of the vATPase requires assembly of the soluble (V(1)) subunits on the membrane subunits (V(0)). It is found that conditions that cause protease activation in the acinar cell also cause assembly of V(1) on V(0). Further, inhibitors of vATPase block this protease activation. Ethanol and butanol sensitize the acinar cell to cholecystokinin-induced zymogen activation; vATPase inhibitors also blocked this activation. Activation of the vATPase may be central to the pathologic activation of proteases in the acinar cell and may also modulate the sensitizing effects of alcohols.

Acute Disease↗
PubMed1984

Pre-natal and post-natal effects of alcohol in the rat--II. Changes in gamma-aminobutyric acid concentration and adenosine triphosphatase activity in the brain.

The effects of chronic alcohol administration during the pre-natal and/or post-natal period on concentration of gamma aminobutyric acid (GABA) in the amygdaloid cortex and striatum and on activities of Na+, K+- and Mg2+ -activated adenosine triphosphatases (ATPases) in the mid-brain and hippocampus were studied. There was a small decrease in the GABA content of both brain regions in those offspring that had received alcohol immediately before, but not in those that were free of the drug at chi the time of death. This suggests that the changes in GABA concentration are due to a direct pharmacological effect of ethanol. A decrease also occurred in the activity of the Mg2+ -activated ATPase in those offspring exposed to alcohol during the period of weaning. This effect could not be attributed to a direct action of the drug, but may be indicative of a longer-term influence of ethanol on membrane transport processes. The increase in the activity of the Na+, K+ -activated ATPase in the mid-brain of rats that were exposed to the drug pre-natally and post-natally and following weaning is probably due to a direct effect of the drug.

Adenosine Triphosphatases↗
PubMed2003

Human corneal endothelial cell expression of Na+,K+-adenosine triphosphatase isoforms.

OBJECTIVE: To determine the expression of alpha subunits and different isozymes of Na+,K+-adenosine triphosphatase (ATPase) in human corneal endothelial cells (HCECs). METHODS: Immunoblot and RNA analysis of Na+,K+-ATPase alpha subunit expression were performed in preparations from HCECs that had been immortalized by transformation with simian virus 40. Na+,K+-ATPase activity was determined by constructing dose-response curves for the ouabain inhibition of Na+,K+-ATPase activity in human corneal endothelial cells. RESULTS: Both messenger RNA analysis and immunoblot studies indicated that HCECs express ATPase catalytic alpha1 and alpha3, but not alpha2 and alpha4, subunits. A limited amount of alpha3 subunit was expressed in HCECs compared with the alpha1 subunit. Biochemical analyses of Na+,K+-ATPase activity revealed 2 independently active Na+,K+-ATPase isoenzymes, a low-affinity site with a kinetic parameter for ouabain inhibition constant (Ki) in the micromolar range and a high-affinity site with a constant Ki in the nanomolar range. These 2 sites may be associated with alpha1 and alpha3 isoforms, respectively, expressed in HCECs. CONCLUSIONS: Human corneal endothelial cells express alpha1 and alpha3 isoforms of Na+,K+-ATPase, and both polypeptides are catalytically competent in these cells. Defining the components of Na+,K+-ATPase in HCECs is an important step toward elucidating the mechanisms that regulate corneal endothelial ionic pump function as well as the pathogenesis of corneal diseases associated with corneal edema.

Cell Line, Transformed↗
PubMed1993

Assembly of the peripheral domain of the bovine vacuolar H(+)-adenosine triphosphatase.

The biosynthesis and assembly of the peripheral sector (V1) of the vacuolar proton-translocating adenosine triphosphatase (V-ATPase) was studied in a bovine kidney epithelial cell line. Monolayer cultures of cells were metabolically radiolabeled with Tran35S-label and the V-ATPase subsequently immunoprecipitated using a monoclonal antibody raised against the bovine brain-coated vesicle proton pump. The V-ATPase immunoprecipitated from the bovine kidney cell line has a subunit composition very similar to that of the bovine brain-coated vesicle proton pump and the V-ATPase prepared from other kidney tissues. Radiolabeling the cells for increasing times showed that the V1 or peripheral portion of the V-ATPase is assembled within 10-15 min; the intact V1V0 complex is also detectable within 10-15 min. Fractionation of the cells into cytosolic and membrane components prior to immunoprecipitation revealed that there is a significant pool of V1 in the cytosol; a similar complex is also found in bovine brain cytosol. Pulse-chase studies suggest that this cytosolic pool is not an obligate precursor for membrane-bound V1V0 and does not exchange with the membrane V1 population at later times. No qualitative differences in assembly were observed when pulse-chase studies were performed at 15 degrees C or in the presence of brefeldin A. This suggests that assembly of V1V0 is probably completed in the endoplasmic reticulum prior to distribution of the enzyme throughout the cell, with a cytosolic pool of V1 of unknown function existing in parallel with the fully assembled complex.

Animals↗
PubMed1980

The influence of adenosine 3',5'-monophosphate upon the activity of the membrane-associated (Ca+ + Mg2+)-dependent adenosine triphosphatase of the human erythrocyte.

The phosphohydrolase activity of the membrane-associated (Ca2+ + Mg2+)-dependent adenosine triphosphatase (ATPase) of the human erythrocyte can be inhibited by micromolar of nanomolar concentrations of cyclic AMP. Millimolar concentrations of cyclic AMP are less effective. The inhibitory effect of cyclic AMP is potentiated in the presence of the phosphodiesterase inhibitor, theophylline.

Ca(2+) Mg(2+)-ATPase↗
PubMed1983

Modulation of the activity of the (Ca2+ + Mg2+)-dependent adenosine triphosphatase of the human erythrocyte.

We previously reported that the activity of the (Ca2+ + Mg2+)-dependent adenosine triphosphatase (ATPase) of the human erythrocyte membrane is inhibited by micromolar or nanomolar concentrations of cyclic AMP. Our further studies have now indicated that the inhibition of (Ca2+ + Mg2+)-dependent phosphohydrolase activity requires the participation of a membrane-associated cyclic AMP-dependent protein kinase and a membrane-associated protein substrate that is distinct from the ATPase itself. We have furthermore, identified a 20 kDa membrane protein which undergoes phosphorylation that is promoted by micromolar, but not millimolar, concentrations of cyclic AMP and which, when phosphorylated, undergoes dephosphorylation that is promoted by Ca2+. We suggest that this membrane component can participate in the modulation of the activity of the (Ca2+ + Mg2+)-dependent ATPase of the human erythrocyte.

Ca(2+) Mg(2+)-ATPase↗
PubMed1994

A conserved epitope on H+,K(+)-adenosine triphosphatase of parietal cells discerned by a murine gastritogenic T-cell clone.

BACKGROUND/AIMS: H+,K(+)-adenosine triphosphatase (H+,K(+)-ATPase) of parietal cells is an organ-specific enzyme recognized by autoantibodies found in human and murine autoimmune gastritis (AIG). Murine AIG can be induced in BALB/c mice by thymectomy 3 days after birth and is a T cell-mediated disease. This study examined the specificity of T cells that cause AIG and the role of H+,K(+)-ATPase in this disease. METHODS: From an AIG mouse, a gastritogenic T-cell clone (II-6) was established, and its reactivity to synthetic peptides of H+,K(+)-ATPase was tested. RESULTS: II-6 cells are CD4+, V beta 14+, and interferon gamma producers. Adoptive transfer of II-6 cells to syngeneic nude mice resulted in AIG without the production of autoantibodies to parietal cells. The II-6 cells were responsive not only to murine but also to human and porcine parietal cells. Their proliferation was also induced by amino acids 891-905 (alpha 891) and 892-906 (alpha 892) of the alpha subunit of porcine and human H+,K(+)-ATPase, respectively. CONCLUSIONS: The T-cell response to a single epitope of H+,K(+)-ATPase, the amino acid sequence of which is conserved among at least three mammals tested, is sufficient to cause AIG. Autoantibodies to parietal cells are not detected in these AIG mice.

Amino Acid Sequence↗
PubMed1985

Effect of Ni2+ on Ca2+-stimulated adenosine triphosphatase in the microsomal fraction of the rat parotid gland in vitro.

Ni2+ inhibited Ca2+-stimulated adenosine triphosphatase activity in the microsomal fraction of the rat parotid gland in vitro. The Ni2+ concentration required for 50% inhibition was 0.45 mM. Inhibition mechanisms of Ni2+ for Ca2+ and ATP were of the competitive type and the noncompetitive type, respectively. The Ki values of Ni2+ for Ca2+ and ATP were 0.52 and 0.59 mM, respectively. The inhibitory effect of Ni2+ was reversible.

Animals↗
PubMed1997

The relationship between airway hyperreactivity (AHR) and sodium, potassium adenosine triphosphatase (Na+,K+ ATPase) enzyme inhibition.

Previous studies have documented the presence of a sodium, potassium adenosine triphosphatase (Na+,K+ ATPase) enzyme inhibitor on platelet membranes and in the plasma of patients with allergy, many of whom historically had airway hyperreactivity (AHR). The purpose of this study was to investigate the relationship between methacholine AHR and Na+,K+ ATPase enzyme inhibition. In the first experiment, 47 adult subjects (13 allergic, 5 potentially allergic, 12 asthmatic, and 17 control subjects) were tested for platelet membrane Na+,K+ ATPase inhibition and AHR. Area under the methacholine dose-response curve (AUC) was expressed as percent baseline FEV1 x log concentration of methacholine (log [mg/ml]) and plotted as a function of the difference in postfreezing and prefreezing platelet membrane Na+,K+ ATPase activities (reflective of membrane-bound inhibitor), which was expressed as nanomoles per microgram of protein per minute (nmol/microg protein/min). A significant (r = -0.44, p < 0.005) negative correlation between the two was detected, such that high levels of AHR (low AUC) were associated with high levels of membrane-bound inhibitor. To test for a causal relationship between the two, the ability of a Na+,K+ ATPase inhibitor to directly influence the level of AHR was determined in a second experiment. Eight allergic and 10 control subjects were administered AHR tests on 2 different days, immediately after inhalation of either nebulized ouabain (1 mg) or placebo in a double-blind fashion. Ouabain versus placebo inhalation decreased the PC20 in four of the patients with allergy. Additionally, ouabain increased methacholine AHR in patients with allergy, as manifested by a lower AUC in seven of the eight patients. In contrast, the mean AUC for the ouabain versus placebo prechallenges did not change significantly in the control group. Finally, a positive correlation was demonstrated between the levels of platelet membrane Na+,K+ ATPase inhibition and bronchial responsiveness to ouabain (r = 0.49, p < 0.05). These results provide both correlative and mechanistic evidence for a causal relationship between Na+,K+ ATPase enzyme inhibition and AHR.

Adult↗
PubMed1996

Effect of haloperidol on the sarcoplasmic reticulum Ca-dependent adenosine triphosphatase.

Several effects of the neuroleptic agent haloperidol on the sarcoplasmic reticulum (SR) Ca-dependent adenosine triphosphatase (Ca-ATPase) and Ca transport are described. Haloperidol inhibits the Ca-ATPase activity in the presence of calcimycin. The effect depends on the conditions of preexposure of the membranes to the drug: the inhibition increases with the preincubation time; Ca and Mg protect the enzyme against the effect of the drug. The inhibitory effect of haloperidol decreases upon increasing [Ca2+], at constant [Mg], and disappears at 20 mM [Mg] for any [Ca2+], and at 0.5 mM [Ca2+] for any [Mg2+]. Haloperidol also inhibits phosphorylation of the enzyme by Pi, and ATP-dependent Ca2+ uptake, in both cases with apparent Ki = 0.10-0.15 mM, and increases the rate of Ca efflux from preloaded vesicles in this concentration range. The results suggest that haloperidol interacts with the catalytic site, interfering with the effect of the divalent catalytic cation, but not at other steps of the enzymatic cycle, where Mg2+ and Ca2+ are also activators. They are consistent with a reaction model where haloperidol interacts with the E2 conformers of the enzyme, with lower affinity for the phosphoenzyme than for the dephospho species. The inhibition of Ca uptake by SR vesicles is ascribed to an increased Ca2+ permeability rather than to the inhibition of the Ca-ATPase, which requires higher concentrations of the drug.

Animals↗
PubMed1967

The sodium-plus-potassium ion-activated adenosine triphosphatase of cerebral microsomal fractions: treatment with disrupting agents.

1. The Na(+)-plus-K(+)-stimulated adenosine triphosphatase [(Na(+),K(+))-ATPase] of microsomal preparations from ox brain was inactivated or diminished in activity by exposure to 2-8m-urea. Similar concentrations of urea diminished the turbidity of the suspensions. 2. Low concentrations (about 2.5mm) of NaATP with the urea gave partial or complete protection of the ATPase, without altering the concomitant change in turbidity. Some protection of the (Na(+),K(+))-ATPase was afforded by tris ATP, but the greatest protection was found with NaATP and in its presence the change in (Na(+),K(+))-ATPase with 3m-urea included a phase in which activity was enhanced by 40%. 3. The protective effect was specific to NaATP: KATP, NaADP, NaAMP and sodium pyrophosphate were without protective effect and in some cases they augmented the action of urea. 4. The turbidity of cerebral microsomal suspensions was diminished also by ultrasonic irradiation; NaATP did not alter this change. After ultrasonic treatment up to 55% of the protein and of the ATPase activity were no longer deposited by centrifugal forces of 4.5x10(6)g-min. 5. Ultrasonic treatment and centrifugation could be carried out with little or no loss of ATPase and ammonium sulphate flocculation of the supernatant then afforded in the first material precipitated a three- to five-fold enrichment of (Na(+),K(+))-ATPase activity. 6. Sodium borohydride and dimethyl sulphoxide also diminished the turbidity of the microsomal fraction but enrichment of the ATPase was not effected by these reagents; ten other compounds were without action on the ATPase. 7. Acetyl phosphate was hydrolysed by the microsomal preparation and this activity was increased by added K(+). Acetyl-phosphatase activity persisted in the ultrasonically treated and ammonium sulphate-fractionated preparations, which were more exacting in their requirements for K(+). 8. The findings are discussed in relation to the mechanism of the (Na(+),K(+))-ATPase.

Journal Article↗
PubMed1991

Calcium adenosine triphosphatase and secretion of koilin membrane in the gizzard of the fowl.

The localization of calcium adenosine triphosphatase (Ca(2+)-ATPase) was determined histo- and ultracytochemically in the gizzard gland cells of the adult domestic fowl. Surface and chief gland cells exhibited faint and inconstant basolateral activity in contrast to basal cells, whose basolateral cell membrane constantly showed deposition on the external side. Intracellular enzyme activity was localized on the luminal aspect of Golgi membranes in all types of gland cells. Lysosomes also reacted positive for Ca(2+)-ATPase. Neither membranes of secretory vesicles nor cortical cytoplasm of the secretory pole exhibited enzyme activity. From these results it is speculated that calcium is not essentially involved in the secretion of the koilin membrane in terms of storage of the secretory material, transport to the secretory surface and release into the lumen. Ca(2+)-ATPase activity rather seems to be related to differentiation and maturation processes and to intracellular storage of Ca2+.

Animals↗
PubMed1985

Erythrocyte sodium/potassium adenosine triphosphatase in thyroid disease and nonthyroidal illness.

Thyroid hormone is known to modulate cell membrane sodium/potassium adenosine triphosphatase (Na/K-ATPase). To determine whether the activity of this enzyme differed in patients with nonthyroidal illness with low levels of circulating thyroid hormones and patients with documented clinical hypothyroidism, we measured Na/K-ATPase activity in red blood cells from patients with hypo- and hyperthyroidism, patients with nonthyroid disease with and without reduced circulating levels of thyroid hormone, and normal subjects. We also assessed whether the activity of this enzyme reflects decreased thyroid hormone action at the cellular level in patients with nonthyroidal illness. Hyperthyroidism was associated with decreased and hypothyroidism with increased erythrocyte Na/K-ATPase activity [142 +/- 24 (+/- SE) and 371 +/- 37 nmol Pi/mg X h; P less than 0.05 and P less than 0.01 compared to normal]. Enzyme activity in cells from patients with nonthyroidal illness and low levels of circulating T3 was significantly higher than that in cells from normal subjects (289 +/- 11 vs. 223 +/- 16 nmol Pi/mg X h; P less than 0.01), but was not significantly different from that in cells from hypothyroid patients. Red cell Na/K-ATPase activity in patients with nonthyroidal illness and normal thyroid function tests (185 +/- 38 nmol Pi/mg X h was indistinguishable from normal values. These data confirm that hyperthyroid patients have decreased red cell Na/K-ATPase activity and provide direct evidence that erythrocyte ATPase activity is increased in hypothyroid patients. The change in enzyme activity in patients with nonthyroidal illness and decreased circulating T3 levels was comparable to that in hypothyroidism. These results suggest that since red cell Na/K-ATPase activity does not distinguish between ill patients with low thyroid function tests and those with hypothyroidism, tissue hypothyroidism may exist in the former group of patients.

Adolescent↗
PubMed1989

Ultrastructural localization of the membrane-bound Mg-adenosine triphosphatase activity in rat meninges.

The distribution of the membrane-bound magnesium ions-dependent adenosine triphosphatase (Mg-ATPase) activity has been studied ultracytochemically in rat meninges by the method of Wachstein and Meisel (1957). A device specially constructed to avoid preparation artefacts has been used to obtain sections from the parietal region of the head. The meninges display an intense though irregularly distributed ATPase activity marked by depositions of electron-dense reaction product (RP) which is almost absent in the outer and middle dural layers. In the borderline zone between dura mater and the arachnoid the RP deposits are found at the outer surface of the inner dural cells and at the contact sites between these cells and the dural neurothelium. The intercellular cleft(s) between the neurothelium and the outer arachnoidal layer, occupied by an "electron-dense band", remains free of RP. The strongest accumulations of reactions granules are observed on the surface of the leptomeningeal cells of the arachnoidal space. In the contact region between the inner arachnoidal and the outer pial layers the distribution of the RP is similar to the one observed in the interface zone dura mater/arachnoid, while the pial cells themselves are definitely reaction-positive. In all meningeal vessels RP is found at the lumenal and abluminal aspects of the endothelium as well as at the cell membranes of the perivascular cells. These results emphasize the importance of the dural neurothelium for the functions of the blood-cerebrospinal fluid (CSF)-barrier between the dural blood vessels and the CSF.

Animals↗
PubMed1987

Effects of aldosterone on rat collecting tubule N-ethylmaleimide-sensitive adenosine triphosphatase.

Acidification in the collecting tubule is thought to be mediated by a proton-translocating adenosine triphosphatase (ATPase), and is modulated by aldosterone. Using an enzymatic microassay, we measured N-ethylmaleimide (NEM)-sensitive ATPase activity in isolated tubules obtained from control rats and rats receiving aldosterone by osmotic minipumps (5 micrograms/100 gm/day for 7 days). In control animals, enzyme activity was higher in cortical than in outer medullary collecting tubules (259 +/- 36 vs. 111 +/- 16 pmol/mm/hr, P less than 0.005, respectively). Prolonged aldosterone administration resulted in an increase in enzyme activity in the outer medullary collecting tubule (274 +/- 39 pmol/mm/hr, P less than 0.005), with no change in the cortical collecting tubule (255 +/- 47 pmol/mm/hr). These findings suggest that prolonged enhancement of acidification by mineralocorticoids is mediated by different mechanisms in the two segments of the rat collecting tubule. Whereas in the outer medullary segment an increase in the activity of NEM-sensitive ATPase facilitates the chronic enhancement in acidification, high basal enzyme activity in the cortical segment and institution of favorable voltage condition by mineralocorticoid treatment may obviate the need to increase enzyme activity.

Aldosterone↗