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At least 973 records · Page 54Linked to original sources
PubMed1990

Flux-dependent increase in the stoichiometry of charge translocation by mitochondrial ATPase/ATP synthase induced by almitrine.

After studying the effects of almitrine, a new kind of ATPase/ATP synthase inhibitor, on two kinds of isolated mammalian mitochondrion, we have observed that: (1) Almitrine inhibits oligomycin-sensitive ATPase; it decreases the ATP/O value of oxidative phosphorylations without any change in the magnitude of delta mu H+. (2) Almitrine increases the mechanistic H+/ATP stoichiometry of ATPase as shown by measuring either (i) the extent of potassium acetate and of potassium phosphate accumulation sustained by ATP utilisation, or (ii) the electrical charge/ATP (K+/ATP) ratio at steady-state of ATPase activity. (3) Rat liver mitochondria are at least 10-times more sensitive to almitrine than beef heart mitochondria. (4) The change in H+/ATP stoichiometry induced by almitrine depends on the magnitude of the flux through ATPase. The inhibitory effect of almitrine on ATPase/ATP synthase complex, as a consequence of such an H+/ATP stoichiometry change, is discussed.

Acetates↗
PubMed1980

Time-dependent changes of calcium influx and efflux rates in rabbit skeletal muscle sarcoplasmic reticulum.

Unfractionated and low buoyant density sarcoplasmic reticulum vesicles released calcium spontaneously after ATP- or acetyl phosphate-supported calcium uptake when internal Ca2+ was stabilized by the use of 50 mM phosphate as calcium-precipitating anion. This spontaneous calcium release could not be attributed to falling Ca2+ concentration outside the vesicles (Ca02+), substrate depletion, ADP accumulation, nonspecific membrane deterioration of the attainment of a high vesicular calcium content. Instead, spontaneous calcium release was directly proportional to Ca02+ at the time that calcium content was maximal. A causal relationship between high Ca02+ and spontaneous calcium release was suggested by the finding that elevation of Ca02+ from less than 1 microM to 3--5 microM increased the rate and extent of calcium release. The spontaneous calcium release was due both to acceleration of calcium efflux and slowing of calcium influx that was not accompanied by a significant change in the rate of ATP hydrolysis. Neither reversal of the transmembrane KCl gradient nor incubation with cation and proton ionophores abolished the spontaneous calcium release. The persistence of calcium release under conditions where the membrane was permeable to both anions and cations makes it unlikely that this phenomenon is due to a changing transmembrane potential. The similarity between the Ca2+ dependence of spontaneous calcium release and of calcium uptake, along with other similarities between these processes, suggest that calcium release is mediated by the calcium pump in these membranes.

Acetates↗
PubMed1983

All-or-none interactions of inhibitors of the plasma membrane ATPase with Saccharomyces cerevisiae.

The inhibitors of the yeast plasma membrane ATPase, Dio-9, miconazole, suloctidil, N,N'-dicyclohexycarbodiimide, triphenyltin and diethylstilbestrol provoke an all-or-none K+ loss from the cells. Some of the K+-depleted cells also show an increased permeability for the dye, Bromophenol blue, indicating that the barrier properties of these cells are drastically changed. Apart from this all-or-none process, a graded loss of K+ is also observed. These observations warn against the use of the inhibitors in studies aimed at evaluating the role of the ATPase in the energy transduction of membrane transport processes of yeasts.

Adenosine Triphosphatases↗
PubMed1984

Possible energization of K+ accumulation into metabolizing yeast by the protonmotive force. Binding correction to be applied in the calculation of the yeast membrane potential from tetraphenylphosphonium distribution.

Membrane potentials of yeast cells, Saccharomyces cerevisiae, calculated from the equilibrium distribution of tetraphenylphosphonium (TPP) between cell-water and medium should be corrected for a contribution due to binding of TPP to intracellular constituents. The magnitude of this correction depends upon the way in which it is determined. In cells permeabilized by boiling, cell-binding is much higher than in cells permeabilized by repeated freezing and thawing. The binding corrections are 75 +/- 1 mV and 49 +/- 7 mV, respectively. The binding correction obtained from TPP distribution between deenergized cells and medium is much lower and amounts to 19 +/- 9 mV. The latter value is probably more reliable. It is supposed that permeabilization of the cells by boiling or repeated freezing and thawing unmasks potential TPP binding groups in the cell. The K+ accumulation into anaerobically metabolizing yeast cells can be accounted for almost quantitatively by a cotransport of protons and K+ ions if the lower binding correction is applied. This means that K+ accumulation into the yeast cell may be driven by the sum of the protonmotive force and the membrane potential.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed1986

Thiocyanate and bromide ions influence the bilayer structural parameters of phosphatidylcholine bilayers.

The influence of monovalent cations and anions on the structural parameters of dipalmitoylphosphatidylcholine (DPPC) bilayers was examined at 25 degrees C using X-ray diffraction. It was shown that monovalent salts, in general, have little effect on lipid packing within the bilayer. However, fully hydrated DPPC bilayers in 1 M KSCN pack in an interdigitated acyl chain phase. This is the first observation of an ion-induced interdigitated bilayer phase in a zwitterionic lipid. In addition, gel state DPPC bilayers in 1 M KBr imbibe approx. 10 A more solvent than bilayers in water. The influence of these same salts on the phase transitions of DPPC bilayers was also examined using high-resolution differential scanning calorimetry. These results are discussed in terms of ion-induced changes in solvent and solvent/bilayer structure.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1986

A study of the mechanism by which inhibitors of the plasmamembrane ATPase enhance uptake of divalent cations in yeast.

The enhancement of divalent cation uptake in yeast provoked by the membrane ATPase inhibitors trifluoperazine, miconazole, compound 48/80, ethidium, DIO-9 and calmidazolium should be ascribed to an increase in cation permeability of the yeast rather than to hyperpolarisation of the yeast cell membrane. For trifluoperazine and miconazole it is unequivocally shown that the cells are hyperpolarized though for miconazole only transiently. Whether the other drugs also hyperpolarize the yeast cells is uncertain. The apparent hyperpolarisation caused by trifluoperazine and miconazole may be attributed to a specific increase in the K+ permeability of the yeast plasmamembrane evoked by these compounds.

Adenosine Triphosphatases↗
PubMed1986

The water and ionic permeability induced by polyene antibiotics across plasma membrane vesicles from Leishmania sp.

An osmotic method has been used to study the effect of the polyene antibiotics amphotericin B, nystatin and candicidin on the water permeability of plasma membranes prepared from Leishmania sp. The effect of amphotericin B on the permeability of Leishmania membranes to a salt such as potassium nitrate was also investigated. A non-linear and saturable enhancement of water and salt permeability was measured with increasing polyene concentrations, which could be adjusted to Hill cooperativity equation. The antibiotic concentrations that induce at 30 degrees C half-maximal effects on the water permeability of Leishmania vesicles were 0.021 microM for candicidin, 0.21 microM for amphotericin B and 1.4 microM for nystatin. At 30 degrees C, the concentration of amphotericin B required to induce half of the maximal effect on the permeability of Leishmania vesicles to potassium nitrate was 1.8 microM. The temperature dependence for amphotericin B, nystatin and candicidin enhancement of the water permeability of Leishmania vesicles was determined by using Q10 data at 20 and 30 degrees C. The estimated activation energies at increasing polyene concentrations display the same general pattern for all three polyene antibiotics investigated, that is, a maximal positive value at about the polyene concentrations required for half-maximal effect. The significance of these results for understanding the mechanisms of action of polyene antibiotics on natural membranes is discussed.

Amphotericin B↗
PubMed1988

Depolarization-induced release of glycine and beta-alanine from plasma membrane vesicles derived from rat brain synaptosomes.

Glycine and beta-alanine actively loaded into brain synaptic plasma membrane vesicles were released into the external medium by using the classical depolarization agents high K+ and veratridine. This release occurs via a Ca2+-independent process. Measurements of membrane depolarization using tetraphenylphosphonium uptake show a close correlation between changes in the membrane potential and stimulation of the efflux process. Results shown herein and previously reported by our group (Aragón, M.C. and Giménez, C. (1986) Biochim. Biophys. Acta 855, 257-264; Agulló, L., Jiménez, B., Aragón, M.C. and Giménez, C. (1986) Eur. J. Biochem. 159, 611-617), suggest that the glycine and beta-alanine transport systems in synaptic plasma membranes are susceptible of modulation by changes in ionic fluxes and hence in the membrane potential, similar to those occurring during depolarization and repolarization.

Action Potentials↗
PubMed1989

The effect of ferricyanide with iodoacetate in calcium-free solution on passive cation permeability in human red blood cells: comparison with the Gardos-effect and with the influence of PCMBS on passive cation permeability.

Freshly prepared human red blood cells incubated with 5 mM ferricyanide, 0.2 mM iodoacetate and 2 mM adenosine in the presence of 5 mM EGTA demonstrate comparable increases in Na+ and K+ permeability (ferricyanide effect). This effect is unrelated to the Ca2+-activated K+ channel (Gardos effect) since influx of Ca2+ from outside the cell is excluded. Also this effect is different from the non-specific Na+ and K+ permeability change elicited by PCMBS. These differences become obvious by using various reagents. For example, A23187 and quinidine exert opposite effects in Gardos and ferricyanide experiments, where A23187 and atebrin react oppositely in the latter and in PCMBS experiments. The ferricyanide effect described here does not involve formation of nonspecific channels. The change in Na+ permeability separately from K+ permeability under certain circumstances suggests a more specific effect.

4-Chloromercuribenzenesulfonate↗
PubMed1990

Enhancement of transmembrane proton conductivity of protonophores by membrane-permeant cations.

The rate of protonophore-mediated decay of pH gradient across lipid vesicular membranes was found to be enhanced by orders of magnitude by valinomycin-K+. Experiments in the presence of gramicidin have shown that the observed rate enhancement by valinomycin-K+ is not due to collapse of the diffusion potential alone. The enhancement of the rate showed hyperbolic dependence on the concentration of valinomycin. Rate enhancement was observed in the presence of the membrane permeant cation tetraphenylphosphonium (TTP+) also. Several factors which might enhance the intrinsic H+ conductivity of protonophores were analyzed. The level of partitioning of the protonophore into the membrane and the pK of membrane-bound protonophores were measured. Valinomycin-K+ did not alter both these parameters significantly. TPP+ increased the partitioning of protonophores and decreased the pK values of membrane-bound protonophores. However, these changes were too small to explain the observed rate enhancements. We suggest that valinomycin-K+ and TPP+ enhance the H+ conductivity of protonophores by increasing the permeability of the ionized form of protonophores by forming an ion pair.

Boron Compounds↗
PubMed1991

A vacuolar ATPase and pyrophosphatase in Acetabularia acetabulum.

Vacuole-rich fractions were isolated from Acetabularia acetabulum by Ficoll step gradient centrifugation. The tonoplast-rich vesicles showed ATP-dependent and pyrophosphate-dependent H(+)-transport activities. ATP-dependent H(+)-transport and ATPase activity were both inhibited by the addition of a specific inhibitor of vacuolar ATPase, bafilomycin B1. A 66 kDa polypeptide present in the preparation cross-reacted with the anti-IgG fractions against the alpha and beta subunits of Halobacterium halobium ATPase and with the antibody against the A subunit (68 kDa subunit) of mung bean vacuolar ATPase. A 56 kDa polypeptide present in the vacuole preparation showed cross-reactivity with the antibody against the B subunit (57 kDa) of mung bean vacuolar ATPase but not with the anti-beta subunit of H. halobium ATPase. A 73 kDa polypeptide cross-reacted with the antibody against inorganic pyrophosphatase of mung bean vacuoles. These results suggest that vacuolar membrane of A. acetabulum equipped energy transducing systems similar to those found in other plant vacuoles.

Acetabularia↗
PubMed1985

Metabolism of cholesteryl ester in monolayers of bovine adrenal cortical cells. Effect of an inhibitor of acyl-CoA: cholesterol acyltransferase.

The effect of Sandoz compound 58-035 on cholesterol metabolism in monolayers of bovine adrenal cortical cells was studied. 58-035 did not inhibit cholesterol ester hydrolase, cholesterol side-chain cleavage, cholesterol synthesis from acetate, or cortisol synthesis in cells stimulated with ACTH or in unstimulated cells. It was, however, an effective inhibitor of formation of cholesteryl ester. The rate of formation of cholesteryl ester in the cells was increased by additional cholesterol derived from mevalonic acid or from the hydrolysis of intracellular lipid droplets. 58-035 caused an increase in the secretion of cortisol from cells maintained on a limited supply of cholesterol from bovine lipoproteins added to the medium when the cells were not stimulated with ACTH. This effect was not observed in stimulated cells. The results suggest that the bovine adrenal cortical cell can direct the flux of exogenous cholesterol very precisely according to its metabolic state.

Adrenal Cortex↗
PubMed1988

Studies on cholesterol esterase in rat adipose tissue: comparison of substrates and regulation of the activity.

Efficiency of substrates for cholesterol esterase (EC 3.1.1.13) assay, and regulation of the activity were investigated in rat epididymal adipose tissue. The activity in the supernatant was activated by cyclic AMP-dependent protein kinase, cyclic AMP, ATP and Mg2+, both with micellar and liposomal substrates. However, the micellar substrate was more suitable for the assay than the liposomal with respect to Vmax and Km. Thus, the micellar substrate was employed. Pretreatment of the supernatant with exogenous cyclic AMP-dependent protein kinase enhanced the activity dose dependently, whereas that with cyclic AMP decreased the activity slightly. The cyclic AMP-dependent protein kinase activity in the assay mixture was within the range which can cause changes in cholesterol esterase activity. These results suggest that the amount of cyclic AMP-dependent protein kinase, rather than the cyclic AMP level, plays an important role in the regulation of cholesterol esterase in tissues with a high cholesterol esterase activity relative to the kinase activity, such as in adipose tissue.

Adenylyl Cyclases↗