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  • 1
    ISSN: 1432-1440
    Keywords: Low-density lipoprotein ; Vitamin E ; Smoking ; Lipid peroxidation ; Atherosclerosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The possible influence of smoking on the low-density lipoprotein (LDL) and its biological activity was investigated. Plasma LDL was prepared from healthy male smokers and nonsmokers, and oxidized with Cu (11) as prooxidant. Oxidized LDL from smokers generated significantly more lipidperoxidation products, so-called thiobarbituric acid reactive substances (TBARS), when compared to oxidized nonsmoker LDL. Analysis of vitamin E levels in LDL obtained from both smokers and nonsmokers revealed that the vitamin E content of smoker LDL was significantly less than that of nonsmoker LDL. The amounts of cholesteryl esters formed in cultured P388. D.1 macrophages were greater in the presence of smoker LDL than with nonsmoker LDL. The data suggest that some of the proatherogenic effects of smoking may be related to oxidative modification of LDL and alteration of its biological activity.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1424
    Keywords: pancreas ; Ca2+ pools ; Ca2+ pump ; acini ; saponin ; secretagogue
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Intracellular ATP-dependent Ca2+ sequestration mechanisms were studied in isolated dispersed rat pancreatic acini following treatment with saponin or digitonin to disrupt their plasma membranes. In the presence of45Ca2+ concentrations 〈10−6 mol/liter, addition of 5 mmol/liter ATP caused a rapid increase in45Ca2+ uptake exceeding the control by fivefold. ADP mimicked the ATP effect by 50 to 60%, whereas other nucleotides such as AMP-PNP, AMP-PCP, CTP, UTP, ITP, GTP, cAMP and cGMP did not. Maximal ATP-promoted Ca2+ uptake was obtained at 10−5 mol/liter Ca2+ uptake by mitochondrial inhibitors was dependent on the Ca2+ concentration, indicating the presence of different Ca2+ storage systems. Whereas the apparent half-saturation constant found for mitochondrial Ca2+ uptake was ∼4.5×10−7 mol/liter, in the presence of antimycin and oligomycin (nonmitochondrial uptake) it was ∼1.4×10−8 mol/liter. In the absence of Mg2+ both ATP- and ADP-promoted Ca2+ uptake was nearly abolished. The Ca2+ ionophore and mersalyl blocked Ca2+ uptake. Electron microscopy showed electrondense precipitates in the rough endoplasmic reticulum of saponintreated cells in the presence of Ca2+, oxalate and ATP, which were absent in intact cells and in saponin-cells without ATP or pretreated with A23187. The data suggest the presence of mitochondrial and nonmitochondrial ATP-dependent Ca2+ storage systems in pancreatic acini. The latter is likely to be located in the rough endoplasmic reticulum.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1424
    Keywords: Thapsigargin ; Vanadate ; Ca2+ pump ; Ca2+ ATPase ; SERCA ; Endoplasmic reticulum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract We have examined the effect of the Ca2+ (Mg2+)-ATPase inhibitors thapsigargin (TG) and vanadate on ATP-dependent 45Ca2+ uptake into IP3-sensitive Ca2+ pools in isolated microsomes from rat pancreatic acinar cells. The inhibitory effect of TG was biphasic. About 40–50% of total Ca2+ uptake was inhibited by TG up to 10 nm (apparent Ki≈4.2 nm, Ca2+ pool I). An additional increase of inhibition up to 85–90% of total Ca2+ uptake could be achieved at 15 to 20 nm of TG (apparent Ki≈12.1 nm, Ca2+ pool II). The rest was due to TG-insensitive contaminating plasma membranes and could be inhibited by vanadate (apparent Ki≈10 μm). In the absence of TG, increasing concentrations of vanadate also showed two phases of inhibition of microsomal Ca2+ uptake. About 30–40% of total Ca2+ uptake was inhibited by 100 μm of vanadate (apparent Ki≈18 μm, Ca2+ pool II). The remaining 60–70% could be inhibited either by vanadate at concentrations up to 1 mm (apparent Ki≈300 μm) or by TG up to 10 nm (Ca2+ pool I). The amount of IP3-induced Ca2+ release was constant at ≈25% over a wide range of Ca2+ filling. About 10–20% remained unreleasable by IP3. Reduction of IP3 releasable Ca2+ in the presence of inhibitors showed similar dose-response curves as Ca2+ uptake (apparent Ki≈ 3.0 nm for IP3-induced Ca2+ release as compared to ≈4.2 nm for Ca2+ uptake at TG up to 10 nm) indicating that the highly TG-sensitive Ca2+ pump fills the IP3-sensitive Ca2+ pool I. At TG concentrations 〉10 nm which blocked Ca2+ pool II the apparent Ki values were ≈11.3 and ≈12.1 nm, respectively. For inhibition by vanadate up to 100 μm the apparent Ki values were ≈18 μm for Ca2+ uptake and ≈7 μm for Ca2+ release (Ca2+ pool II). At vanadate concentrations up to 1 mm the apparent Ki values were ≈300 and ≈200 μm, respectively (Ca2+ pool I). Both Ca2+ pools I and II also showed different sensitivities to IP3. Dose-response curves for IP3 in the absence of inhibitors (control) showed an apparent Km value for IP3 at 0.6 μm. In the presence of TG (inhibition of Ca2+ pool I) the curve was shifted to the left with an apparent Km for IP3 at 0.08 μm. In the presence of vanadate (inhibition of Ca2+ pool II), the apparent Km for IP3 was 2.1 μm. These data allow the conclusion that there are at least three different Ca2+ uptake mechanisms present in pancreatic acinar cells: TG- and IP3 insensitive but highly vanadate-sensitive Ca2+ uptake occurs into membrane vesicles derived from plasma membranes. Two Ca2+ pools with different TG-, vanadate- and IP3-sensitivities are most likely located in the endoplasmic reticulum at different cell sites, which could have functional implications for hormonal stimulation of pancreatic acinar cells.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 29 (1976), S. 185-203 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Secretagogues of pancreatic enzyme secretion, the hormones pancreozymin, carbamylcholine, gastrin I, the octapeptide of pancreozymin, and caerulein as well as the Ca++-ionophore A 23187 stimulate45Ca efflux from isolated pancreatic cells. The nonsecretagogic hormones adrenaline, isoproterenol, secretin, as well as dibutyryl cyclic adenosine 3′,5′-monophosphate and dibutyryl cyclic guanosine 3′,5′-monophosphate have no effect on45Ca efflux. Atropine blocks the stimulatory effect of carbamylcholine on45Ca efflux completely, but not that of pancreozymin. A graphical analysis of the Ca++ efflux curves reveals at least three phases: a first phase, probably derived from Ca++ bound to the plasma membrane; a second phase, possibly representing Ca++ efflux from cytosol of the cells; and a third phase, probably from mitochondria or other cellular particles. The Ca++ efflux of all phases is stimulated by pancreozymin and carbamylcholine. Ca++ efflux is not significantly effected by the presence or absence of Ca++ in the incubation medium. Metabolic inhibitors of ATP production, Antimycin A and dinitrophenol, which inhibit Ca++ uptake into mitochondria, stimulate Ca++ efflux from the isolated cells remarkably, but inhibit the slow phase of Ca++ influx, indicating the role of mitochondria as an intracellular Ca++ compartment. Measurements of the45Ca++ influx at different Ca++ concentrations in the medium reveal saturation type kinetics, which are compatible with a carrier or channel model. The hormones mentioned above stimulate the rate of Ca++ translocation. The data suggest that secretagogues of pancreatic enzyme secretion act by increasing the rate of Ca++ transport most likely at the level of the cell membrane and that Ca++ exchange diffusion does not contribute to the45Ca++ fluxes.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 36 (1977), S. 253-279 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Pancreas of the cat was fractionated into its subcellular components by centrifugation through an exponential ficoll-sucrose density gradient in a zonal rotor. This enables a preparation of four fractions enriched in plasma membranes, endoplasmic reticulum, mitochondria and zymogen granules, respectively. The first fraction, enriched by 9- to 15-fold in the plasma membrane marker enzymes, hormone-stimulated adenylate cyclase, (Na+K+)-ATPase, and 5′-nucleotidase, is contaminated by membranes derived from endoplasmic reticulum but is virtually free from mitochondrial and zymogen-granule contamination. The second fraction from the zonal gradient shows only moderate enrichment of the above marker enzymes but contains a considerable quantity of plasma membrane marker enzymes and represents mostly rough endoplasmic reticulum. The third fraction contains the bulk of mitochondria and the fourth mainly zymogen granules as assessed by electron microscopy and marker enzymes for both mitochondria and zymogen granules, namely succinic dehydrogenase, trypsin and amylase. Further purification of the plasma membrane fractions by differential and sucrose step-gradient centrifugation yields plasma membrane enriched 40-fold in basal and hormone-stimulated adenylate cyclase and (Na+K+)-ATPase.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 36 (1977), S. 281-295 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A membrane and zymogen granule fraction of cat pancreas has been purified on an exponential ficoll-sucrose gradient in a zonal rotor. A Ca++-dependent interaction between the membranes labelled with125I or14C-p-chloromercuribenzoate or N-ethyl(2,3-14C)maleimide and zymogen granules has been observed by measuring the amount of membrane protein, enzymes, and peptides which stay associated with the granules after centrifugation through a 31% sucrose cushion. The interaction was a function of the Ca++ concentration, starting at 1×10−6 m and being saturated at 2×10−5 m of free Ca++ (apparentK m =6.5×10−6 m), and showed preference for Ca++ over other divalent cations with a selectivity sequence (at 0.5mm of total cation concentration): Ca++ 100, Mg++ 35, Ba++ 25, Sr++ 20. The interaction between membranes and granules was specific for cat pancreatic membranes as opposed to cat liver membranes, and for pancreatic zymogen granules as opposed to pancreatic mitochondria. Only 30% of the membrane fraction was bound at saturating levels of zymogen granules and the bound fraction contained alkaline phosphatase, but not other pancreatic plasma membrane markers such as adenylate cyclase or 5′-nucleotidase. After the interaction, removal of Ca++ by the calcium chelator EGTA only partially (about 30%) reversed binding of labelled membranes to the zymogen granules. The process appears to be dependent on the membrane proteins, since brief trypsinization of membranes prior to the assay completely abolished the Ca++-induced interaction. It is concluded that 1) the observed binding may reflect an initial Ca++-dependent event in the process of fusion of zymogen granules with the apical plasma membranes of acinar cells, and 2) protein recognition sites on the interacting membranes are essential for this process.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 38 (1978), S. 333-346 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Transport of alanine was studied in isolated plasma membrane vesicles from cat pancreas using a rapid filtration technique. The uptake is osmotically sensitive and the kinetics ofl-alanine transport are biphasic showing a saturable and a nonsaturable component. The saturable component is seen only when a sodium gradient directed from the medium to the vesicular space is present. Under this condition an overshooting uptake ofl-but not ofd-alanine occurs. The Na+ gradient stimulated uptake ofl-alanine is inhibited byl-serine andl-leucine and stimulated when the membrane vesicles had been preloaded withl-alanine,l-serine orl-leucine. The ionophore monensin inhibits stimulation of uptake caused by a sodium gradient. In the presence of valinomycin or carbonyl cyanidep-trifluoromethoxyphenylhydrazone (CFCCP), the sodium-dependent transport is augmented in vesicles preloaded with K2SO4 or H+ ions (intravesicular pH 5.5), respectively. In the presence of different anions, the Na+-dependent transport is stimulated according to increasing anionic penetration through membranes (lipid solubility). We conclude that a sodium dependent electrogenic amino acid transport system is present in pancreatic plasma membranes.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 87 (1985), S. 107-119 
    ISSN: 1432-1424
    Keywords: Na+/Ca2+ countertransport ; plasma membrane ; pancreatic acinar cells ; amiloride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The presence of a coupled Na+/Ca2+ exchange system has been demonstrated in plasma membrane vesicles from rat pancreatic acinar cells. Na+/Ca2+ exchange was investigated by measuring45Ca2+ uptake and45Ca2+ efflux in the presence of sodium gradients and at different electrical potential differences across the membrane (=Δϕ) in the presence of sodium. Plasma membranes were prepared by a MgCl2 precipitation method and characterized by marker enzyme distribution. When compared to the total homogenate, the typical marker for the plasma membrane, (Na++K+)-ATPase was enriched by 23-fold. Markers for the endoplasmic reticulum, such as RNA and NADPH cytochromec reductase, as well as for mitochondria, the cytochromec oxidase, were reduced by twofold, threefold and 10-fold, respectively. For the Na+/Ca2+ countertransport system, the Ca2+ uptake after 1 min of incubation was half-maximal at 0.62 μmol/liter Ca2+ and at 20 mmol/liter Na+ concentration and maximal at 10 μmol/liter Ca2+ and 150 mmol/liter Na+ concentration, respecitively. When Na+ was replaced by Li+, maximal Ca2+ uptake was 75% as compared to that in the presence of Na+. Amiloride (10−3 mol/liter) at 200 mmol/liter Na+ did not inhibit Na+/Ca2+ countertransport, whereas at low Na+ concentration (25 mmol/liter) amiloride exhibited dose-dependent inhibition to be 62% at 10−2 mol/liter. CFCCP (10−5 mol/liter) did not influence Na+/Ca2+ countertransport. Monensin inhibited dose dependently; at a concentration of 5×10−6 mol/liter inhibition was 80%. A SCN− or K+ diffusion potential (=Δϕ), being positive at the vesicle inside, stimulated calcium uptake in the presence of sodium suggesting that Na+/Ca2+ countertransport operates electrogenically, i.e. with a stoichiometry higher than 2 Na+ for 1 Ca2+. In the absence of Na+, Δϕ did not promote Ca2+ uptake. We conclude that in addition to ATP-dependent Ca2+ outward transport as characterized previously (E. Bayerdörffer, L. Eckhardt, W. Haase & 1. Schulz, 1985,J. Membrane Biol. 84:45–60) the Na+/Ca2+ countertransport system, as characterized in this study, represents a second transport system for the extrusion of calcium from the cell. Furthermore, the high affinity for calcium suggests that this system might participate in the regulation of the cytosolic free Ca2+ level.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 81 (1984), S. 241-253 
    ISSN: 1432-1424
    Keywords: stimulus secretion coupling ; pancreatic acinar cells ; intracellular calcium stores ; calcium transport ; inositol phosphates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary We have previously shown that inositol-1,4,5-trisphosphate (IP3) releases Ca2+ from an intracellular calcium store in permeabilized acinar cells of rat pancreas (H. Streb et al., 1983,Nature (London) 306:67–69). This observation suggests that IP3 might provide the missing link between activation of the muscarinic receptor and Ca2+ release from intracellular stores during stimulation. In order to localize the intracellular IP3-sensitive calcium pool, IP3-induced Ca2+ release was measured in isolated subcellular fractions. A total homogenate was prepared from acinar cells which had been isolated by a collagenase digestion method. Endoplasmic reticulum was separated from mitochondria, zymogen granules and nuclei by differential centrifugation. Plasma membranes and endoplasmic reticulum were separated by centrifugation on a sucrose step gradient or by precipitation with high concentrations of MgCl2. IP3-induced Ca2+ release per mg protein in the total homogenate was the same as in leaky cells and was sufficiently stable to make short separation procedures possible. In fractions obtained by either differential centrifugation at 7000×g, sucrose-density centrifugation, or MgCl2 precipitation there was a close correlation of IP3-induced Ca2+ release with the endoplasmic reticulum markers ribonucleic acid (r=0.96, 1.00, 0.91, respectively) and NADPH cytochromec reductase (r=0.63, 0.98, 090, respectively). In contrast, there was a clear negative correlation with the mitochondrial markers cytochromec oxidase (r=−0.64) and glutamate dehydrogenase (r=−0.75) and with the plasma membrane markers (Na++K+)-ATPase (r=−0.81) and alkaline phosphatase (r=−0.77) in all fractions analyzed. IP3-induced Ca2+ release was distributed independently of zymogen granule or nuclei content of the fractions as assessed by electron microscopy. The data suggest that inositol-1,4,5-trisphosphate releases Ca2+ from endoplasmic reticulum in pancreatic acinar cells.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 84 (1985), S. 45-60 
    ISSN: 1432-1424
    Keywords: electrogenic Ca2+ transport ; plasma membrane ; rough endoplasmic reticulum ; pancreatic acinar cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary ATP-dependent45Ca2+ uptake was investigated in purified plasma membranes from rat pancreatic acinar cells. Plasma membranes were purified by four subsequent precipitations with MgCl2 and characterized by marker enzyme distribution. When compared to the total homogenate, typical marker enzymes for the plasma membrane, (Na+,K+)-ATPase, basal adenylate cyclase and CCK-OP-stimulated adenylate cyclase were enriched by 43-fold, 44-fold, and 45-fold, respectively. The marker for the rough endoplasmic reticulum was decreased by fourfold compared to the total homogenate. Comparing plasma membranes with rough endoplasmic reticulum, Ca2+ uptake was maximal with 10 and 2 μmol/liter free Ca2+, and half-maximal with 0.9 and 0.5 μmol/liter free Ca2+. It was maximal at 3 and 0.2 mmol/liter free Mg2+ concentration, at an ATP concentration of 5 and 1 mmol/liter, respectively, and at pH 7 for both preparations. When Mg2+ was replaced by Mn2+ or Zn2+ ATP-dependent Ca2+ uptake was 63 and 11%, respectively, in plasma membranes; in rough endoplasmic reticulum only Mn2+ could replace Mg2+ for Ca2+ uptake by 20%. Other divalent cations such as Ba2+ and Sr2+ could not replace Mg2+ in Ca2+ uptake. Ca2+ uptake into plasma membranes was not enhanced by oxalate in contrast to Ca2+ uptake in rough endoplasmic reticulum which was stimulated by 7.3-fold. Both plasma membranes and rough endoplasmic reticulum showed cation and anion dependencies of Ca2+ uptake. The sequence was K+〉Rb+〉Na+〉Li+〉choline+ in plasma membranes and Rb+≥K+≥Na+〉Li+〉choline+ for rough endoplasmic reticulum. The anion sequence was Cl−≥Br−≥I−〉SCN−〉NO 3 − 〉isethionate− 〉cyclamate−〉gluconate−〉SO 4 2− ≥glutarate− and Cl−〉Br〉gluconate〉SO 4 2− 〉NO 3 − 〉I−〉cyclamate−≥SCN−, respectively. Ca2+ uptake into plasma membranes appeared to be electrogenic since it was stimulated by an inside-negative K+ and SCN diffusion potential and inhibited by an inside-positive diffusion potential. Ca2+ uptake into rough endoplasmic reticulum was not affected by diffusion potentials. We assume that the Ca2+ transport mechanism in plasma membranes as characterized in this study represents the extrusion system for Ca2+ from the cell that might be involved in the regulation of the cytosolic Ca2+ level.
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