scholarly journals Na+ modulates carrier-mediated Fe2+ transport through the erythroid cell membrane

1991 ◽  
Vol 275 (3) ◽  
pp. 635-638 ◽  
Author(s):  
A Egyed
Keyword(s):  
Cell Membrane ◽  
Choline Chloride ◽  
Maximum Velocity ◽  
Erythroid Cell ◽  
Exchange System ◽  
Ph Optimum ◽  
Low Concentrations ◽  
Free Choline ◽  
Uptake Process ◽  
Rabbit Reticulocytes

The effects of univalent cations on Fe2+ uptake by rabbit reticulocytes have been studied. The rate of Fe2+ uptake was almost identical when measured in Na(+)-free choline chloride or KCl medium. Na+ but not Li+ inhibited Fe2+ uptake even at relatively low concentrations (2.5-20 mM) in these media. In contrast to this effect of extracellular Na+, the rate of Fe2+ uptake was facilitated by an increase in the intracellular Na2+ concentration in the range 5-40 mM, suggesting that intracellular Na+ is required for the uptake process. This effect also appears to be specific for Na+. Amiloride inhibited Fe2+ uptake in KCl (or in choline chloride), but had little if any effect in NaCl. Therefore a Na(+)- and amiloride-sensitive and a Na(+)- and amiloride-insensitive component can be distinguished. The two components differ in maximum velocity and pH optimum, but not in their apparent affinity for Fe2+. The ineffectiveness of selective inhibitors excludes the involvement of the Na+/H+ or Na+/Ca2+ exchange mechanisms. To account for the results presented in this work, a Na+/Fe2+ exchange system in the erythroid cell membrane is proposed.

Kinetics of the Na+-H+ antiporter as assessed by the change in intracellular pH in MDCK cells

1986 ◽  
Vol 251 (4) ◽  
pp. C558-C562 ◽  
Author(s):  
A. M. Selvaggio ◽  
J. H. Schwartz ◽  
H. H. Bengele ◽  
E. A. Alexander
Keyword(s):  
Intracellular Ph ◽  
Mdck Cells ◽  
Choline Chloride ◽  
Maximum Velocity ◽  
Ph Sensitive ◽  
Proton Efflux ◽  
Saturation Kinetics ◽  
Free Choline ◽  
Kinetics Of ◽  
Phi Regulation

The Na+-H+ antiporter regulates both H+ secretion and cell pH in renal epithelia. The present study was designed to further define the Na+ dependency and kinetics of proton efflux in MDCK cells. Intracellular pH (pHi) was determined with a pH-sensitive fluorescent probe, 2,7-bis-carboxyethyl-5,6-carboxyfluorescein (BCECF). Data were obtained from confluent monolayers grown on plastic cover slips and studied in media free of added CO2 and HCO-3, pH = 7.2 (pHo). Monolayers in NaCl maintain a pHi of 7.48 +/- 0.03 (n = 13). When cells were acidified with NH4Cl, pHi decreased to 6.73 +/- 0.07 (n = 10) and remained stable in Na+-free choline chloride. When monolayers were subsequently exposed to NaCl, pHi increased 0.28 +/- 0.04 pH units/min. Amiloride (2.5 mM) inhibited this Na+-dependent rise in pHi by more than 75%. The rate of pHi recovery after exposure to Na+ exhibited saturation kinetics; the apparent Km(Na) was 30.4 +/- 4.2 mM and maximum velocity was 107.1 +/- 17.1 delta [H+]i nmol X l-1 X min-1. We conclude that pHi regulation in the MDCK cell is in part mediated by a Na+-H+ antiporter, and the kinetics of this process can be reliably assessed by the pH-sensitive fluorometric probe, BCECF.

Uptake of thyroxine in the human choriocarcinoma cell line JAR

1995 ◽  
Vol 146 (2) ◽  
pp. 233-238 ◽  
Author(s):  
A M Mitchell ◽  
S W Manley ◽  
E J Payne ◽  
R H Mortimer
Keyword(s):  
Cell Membrane ◽  
Cell Line ◽  
Maximum Velocity ◽  
Potassium Cyanide ◽  
Protein Uptake ◽  
Uptake Rates ◽  
Uptake Process ◽  
Specific Uptake ◽  
Intracellular Energy ◽  
Choriocarcinoma Cell Line

Abstract We have studied the uptake of 125I-thyroxine (125I-T4) in the human choriocarcinoma cell line JAR. Uptake of 125I-T4 was time-dependent, stereospecific and reversible, with a saturable component of 33% after 120 min of incubation. Kinetic analysis of the initial specific uptake rates indicated the presence of a single uptake process with a Michaelis constant of 59·4 ± 13·9 nm (n=12) and maximum velocity of 0·29 ± 0·06 pmol/min per mg protein. Uptake was dependent on intracellular energy as, in the presence of 2 mm potassium cyanide, saturable uptake was reduced to 60·6 ± 8·5% (n=4) of control uptake. Uptake was also temperature-dependent. Saturable 125I-T4 uptake after 60 min of incubation was 26·1 ± 3·0% at 25 °C (n=6) and 27·3 ± 5·7% at 4 °C of control uptake at 37 °C. Ouabain did not inhibit 125I-T4 uptake indicating that the uptake was independent of the Na gradient across the cell membrane. Although T4 uptake was stereospecific, as d-T4 failed to inhibit 125I-l-T4 uptake, it was not specific for T4, as tri-iodothyronine (T3) and reverse T3 also inhibited 125I-T4 uptake. We conclude that JAR cells have a saturable, stereospecific and reversible membrane transport mechanism for T4 which is dependent on intracellular energy, but independent of the Na+ gradient across the cell membrane. Journal of Endocrinology (1995) 146, 233–238

scholarly journals A shift in the optimum pH of phospholipase D produced by activating long-chain anions

1969 ◽  
Vol 112 (5) ◽  
pp. 795-799 ◽  
Author(s):  
R. H. Quarles ◽  
R. M. C. Dawson
Keyword(s):  
Phosphatidic Acid ◽  
Phospholipase D ◽  
Activity Profile ◽  
Ph Optimum ◽  
Surface Ph ◽  
Electrophoretic Mobilities ◽  
Low Concentrations ◽  
Optimum Ph ◽  
Long Chain

1. The activity of phospholipase D (phosphatidylcholine phosphatidohydrolase, EC 3.1.4.4) towards ultrasonically treated phosphatidylcholine or large phosphatidylcholine particles activated with ether was maximal near pH5, and there was little activity above pH6. 2. When the enzyme was activated by the addition of phosphatidic acid to large phosphatidylcholine particles the pH optimum was shifted to pH6·5 irrespective of the amount of activator added. 3. When the enzyme was activated with low concentrations of dodecyl sulphate the pH optimum was 5·5 with little activity above pH6. With higher concentrations of dodecyl sulphate the pH–activity profile was shifted upwards towards a pH optimum of 6·5–6·6, the magnitude of the shift depending on the extent of the hydrolysis. 4. The shifts in the pH–activity profiles cannot be correlated with changes in the ‘surface pH’ of the substrate particles calculated from the measurement of their ζ-potentials (electrophoretic mobilities).

Studies of the uptake of macromolecules by cells. I. Uptake of proteins by cells of the Ehrlich–Lettré ascites carcinoma

1968 ◽  
Vol 46 (12) ◽  
pp. 1443-1450 ◽  
Author(s):  
Y. C. Choi ◽  
E. R. M. Kay
Keyword(s):  
Nucleic Acid ◽  
Cell Membrane ◽  
Binding Sites ◽  
Specific Binding ◽  
Protein Uptake ◽  
Specific Binding Sites ◽  
Model Protein ◽  
Uptake Process ◽  
Kinetics Of ◽  
Protein Treatment

The uptake of protein by cells of the Ehrlich–Lettré ascites carcinoma was characterized kinetically by using hemoglobin as a model protein. An attempt was made to show that the process is not an artefact due to nonspecific adsorption of protein to the cell membrane. The kinetics of the uptake process suggested that an interaction exists between the exogenous protein and specific binding sites on the membrane. Acetylation of hemoglobin enhanced the rate of uptake of this protein. Treatment of cells with neuraminidase, phospholipase A, and Pronase resulted in an inhibition of protein uptake. The experimental evidence for the uptake of hemoglobin was supported by evidence that L-serine-U-14C-labelled hemoglobin is transported into the cytoplasm and utilized subsequently, resulting in labelling of the nucleic acid nucleotides.

Pancreatic beta-cell electrical activity: the role of anions and the control of pH

1983 ◽  
Vol 244 (3) ◽  
pp. C188-C197 ◽  
Author(s):  
G. T. Eddlestone ◽  
P. M. Beigelman
Keyword(s):  
Membrane Potential ◽  
Cell Membrane ◽  
Beta Cell ◽  
Pancreatic Beta Cell ◽  
Proton Exchange ◽  
Disulfonic Acid ◽  
Control Mechanisms ◽  
Exchange System ◽  
Sodium Proton Exchange

The influence of chloride on the mouse pancreatic beta-cell membrane potential and the cell membrane mechanisms controlling intracellular pH (pHi) have been investigated using glass microelectrodes to monitor the membrane potential. It has been shown that chloride is distributed passively across the beta-cell membrane such that chloride potential is equal to the membrane potential. Withdrawal of perifusate chloride or bicarbonate and the application of the drugs 4-acetamido-4'-isethiocyanostilbene-2,2'-disulfonic acid (SITS) and probenecid, both blockers of transmembrane anion movement, have been used to establish that a chloride-bicarbonate exchange system is operative in the cell membrane and that it is one of the control mechanisms of pHi. Amiloride, a specific blocker of the transmembrane sodium proton exchange, has been used to demonstrate that this mechanism is also operative in the beta-cell membrane in the control of pHi. The hypothesis that the calcium-activated potassium permeability is proton sensitive at an intracellular site, a fall in pHi causing a fall in permeability and an increase in pHi causing an increase in permeability, has been used to explain many of the effects observed in this study.

scholarly journals CATION TRANSPORT IN YEAST

1956 ◽  
Vol 39 (5) ◽  
pp. 687-704 ◽  
Author(s):  
Ernest C. Foulkes
Keyword(s):  
Cell Membrane ◽  
Dissociation Constant ◽  
Concentration Gradient ◽  
Cation Transport ◽  
K Uptake ◽  
Present Evidence ◽  
Inhibitor Complex ◽  
Maximum Value ◽  
Low Concentrations ◽  
K Transport

1. The distribution of azide added to suspensions of bakers' yeast was studied under various conditions. The recovery of azide was estimated in the volume of water into which low concentrations of electrolytes can readily diffuse (anion space). Considerable azide disappeared from this anion space. 2. The incomplete recovery of azide in the anion space is due to its uptake by the cells. This uptake occurs against a concentration gradient at 0°C., and is attributed to binding of azide by cell constituents. 3. Confirmatory evidence is presented that one such constituent is the K carrier in the cell membrane. The azide inhibition of K transport is not mediated by inhibition of cytochrome oxidase in the mitochondria. 4. From the amount of combined azide and the experimentally determined dissociation constant of the K carrier-inhibitor complex, the maximum value for the concentration of this carrier is calculated as 0.1 µM/gm. yeast. 5. The addition of glucose and PO4 causes a secondary K uptake which is not azide-sensitive and is clearly distinct from the primary, azide-sensitive mechanism. 6. The existence of a separate carrier responsible for Na extrusion is reconsidered. It is concluded that present evidence does not necessitate the assumption that such a carrier is active in yeast.

Anion-stimulated ATPase activity of brush border from rat small intestine.

1979 ◽  
Vol 236 (1) ◽  
pp. E70 ◽  
Author(s):  
M H Humphreys ◽  
L Y Chou
Keyword(s):  
Alkaline Phosphatase ◽  
Atpase Activity ◽  
Brush Border ◽  
Atp Hydrolysis ◽  
Intestinal Transport ◽  
Mitochondrial Enzymes ◽  
Intestinal Alkaline Phosphatase ◽  
Ph Optimum ◽  
Low Concentrations ◽  
Small Intestinal

Differential centrifugation of rat small intestinal homogenates produced a crude brush border (BB) fraction that was enriched 15-fold for the marker enzymes, alkaline phosphatase and sucrase; contamination with mitochondrial enzymes, monoamine oxidase and succinate dehydrogenase, was minimal. ATP hydrolysis by this BB fraction was stimulated by addition of several anions to the incubation medium: HCO3 and Cl were equally effective in this regard, with NO3, NO2, SO4, and acetate being less stimulatory. SCN and CNO inhibited ATPase activity, whereas the divalent anion SO3 was stimulatory at low concentrations (less than 25 mM) but inhibitory at 100 mM. Maximum anion stimulation was observed at a Mg concentration of 0.5 mM, and pH optimum was 8.5. Kinetic analysis showed that HCO3 increased the Vmax without altering the Km for ATP; the Ka for this effect of HCO3 was 35 mM. This enzyme activity was completely inhibited by 20 mM L-phenylalanine, 10 mM L-cysteine, and 3 mM EDTA, compounds that also inhibited intestinal alkaline phosphatase. These results demonstrate the presence of anion-stimulated ATPase activity in rat small intestinal brush border and suggest that this activity may be related to intestinal alkaline phosphatase. The role of this enzyme in intestinal transport is not known, but could relate to the regulation of intestinal absorption and secretion.

Furosemide-sensitive thallium fluxes in smooth muscle of rabbit uterus

1983 ◽  
Vol 245 (6) ◽  
pp. F778-F783
Author(s):  
A. Johns ◽  
S. V. Cutshaw
Keyword(s):  
Smooth Muscle ◽  
Binding Sites ◽  
Rank Order ◽  
Chloride Concentration ◽  
Cation Binding ◽  
Exchange System ◽  
Total Uptake ◽  
Low Concentrations ◽  
Chloride Pump ◽  
High Concentrations

The furosemide-sensitive uptake of thallium represents approximately equal to 50% of the total uptake of thallium by rabbit uterus and requires Cl- and Na+. The furosemide-sensitive uptake of thallium is stimulated by other ions at low concentrations with the rank order Li+ greater than Tl+ greater than K+ = Rb+ greater than Cs+ and is inhibited by these ions at high concentrations with the rank order Tl+ greater than K+ = Rb+ greater than Cs+ greater than Li+, suggesting multiple cation binding sites on the carrier. Uptake of 36Cl- is inhibited by furosemide in the presence of ouabain. Thallium efflux and 36Cl efflux in the presence of ouabain is inhibited by furosemide. The chloride concentration regulates the proportion of thallium uptake that is ouabain sensitive and furosemide sensitive without altering the total uptake. It is suggested that the furosemide-sensitive uptake of thallium reflects a Na+-Cl- -K+ exchange system that could be classified as a cotransport or countertransport of any two of these ions and also could be the smooth muscle chloride pump.

scholarly journals Lipid synthesis in human erythroid cells: the effect of sickling

Blood ◽  
1976 ◽  
Vol 47 (2) ◽  
pp. 189-195 ◽  
Author(s):  
TA Lane ◽  
SK Ballas ◽  
ER Burka
Keyword(s):  
Cell Membrane ◽  
Neutral Lipid ◽  
Sickle Cell Anemia ◽  
De Novo ◽  
Membrane Lipids ◽  
Membrane Damage ◽  
Lipid Synthesis ◽  
Membrane Lipid ◽  
Erythroid Cell ◽  
Cell Membrane Damage

Abstract Human reticulocytes are capable of synthesizing membrane lipids from 14C-glycerol de novo. In both sickle and nonsickle reticulocytes the majority of 14C-glycerol was incorporated into phospholipids, primarily phosphatidylserine and phosphatidylcholine. Incorporation into sphingomyelin was minimal. The most abundant neutral lipid synthesized was triglyceride. In the absence of sickling, the rate of lipid synthesis in sickle reticulocytes was similar to that of nonsickle reticulocytes. With the induction of sickling under anoxic conditions sickle reticulocytes showed a prompt increase in the rate of lipid synthesis to an average of 69% above control values, while nonsickle reticulocytes under similar conditions decreased the rate of lipid synthesis. An increase in the rate of membrane lipid synthesis is associated in the mammalian erythroid cell with cell membrane damage. The findings further confirm that lesions of the erythroid cell membrane in sickle cell anemia are secondary to the sickling process itself.

Characterization of CDPdiacylglycerol hydrolase in mitochondrial and microsomal fractions from rat lung

1988 ◽  
Vol 66 (5) ◽  
pp. 425-435 ◽  
Author(s):  
Amy Mok ◽  
Tanya Wong ◽  
Octavio Filgueiras ◽  
Paul G. Casola ◽  
Don W. Nicholson ◽  
...  
Keyword(s):  
Divalent Cations ◽  
Mitochondrial Fraction ◽  
Liver Mitochondria ◽  
Inhibitory Effect ◽  
Mitochondrial Activity ◽  
Rat Lung ◽  
Ph Optimum ◽  
Low Concentrations ◽  
Mercuric Ions

CDPdiacylglycerol pyrophosphatase (E. C. 3.6.1.26) activity has been examined in rat lung mitochondrial and microsomal fractions. While the mitochondrial hydrolase exhibited a broad pH optimum from pH 6–8, the microsomal activity decreased rapidly above pH 6.5. Apparent Km values of 36.2 and 23.6 μM and Vmax values of 311 and 197 pmol∙min−1∙mg protein−1 were observed for the mitochondrial and microsomal preparations, respectively. Addition of parachloromercuriphenylsulphonic acid led to a marked inhibition of the microsomal fraction but slightly stimulated the mitochondrial activity at low concentrations. Mercuric ions were inhibitory with both fractions. Although biosynthetic reactions utilizing CDPdiacylglycerol require divalent cations, addition of Mg2+, Mn2+, Ca2+, Zn2+, Co2+, and Cu2+ all inhibited the catabolic CDPdiacylglycerol hydrolase activity in both fractions. EDTA and EGTA also produced an inhibitory effect, especially with the mitochondrial fraction. Although addition of either adenine or cytidine nucleotides led to a decrease in activity with both fractions, the marked susceptibility to AMP previously reported for this enzyme in Escherichia coli membranes, guinea pig brain lysosomes, and pig liver mitochondria was not observed. These results indicate that rat lung mitochondria and microsomes contain specific CDPdiacylglycerol hydrolase activities, which could influence the rate of formation of phosphatidylinositol and phosphatidylglycerol for pulmonary surfactant.

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