Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Valinomycin”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12Linked to original sources
PubMed1975

Models of ionic transport in biological membranes. Raman spectroscopy as a probe of valinomycin, gramicidin A', and rhodopsin conformations.

There is evidence that membrane proteins can serve as the functional units of ionic transport in biological membranes. Laser Raman spectroscopy has been used to probe specific molecular interactions inside two models of transport membrane proteins, valinomycin and gramicidin A. Conformational changes of these molecules, as well as specific interactions with ions, can be detected and may help elucidate how membrane transport proteins such as Na+ minus K+ ATPase and rhodopsin function. Resonance Raman spectroscopy has also been used to study conformational changes and protein-chromophore interactions in rhodopsin, the membrane protein that acts as the primary unit of visual excitation in the eye.

Adenosine Triphosphatases↗
PubMed1993

In vitro interaction of liposomal valinomycin and platinum analogs: cytotoxic and cytokinetic effects.

Cisplatin is the most active agent in the chemotherapy of ovarian cancer and this activity can be enhanced by liposomal valinomycin (MLV-VM) in vitro. To test whether MLV-VM is capable of augmenting the cytotoxic and cytokinetic effects of other platinum analogs, drug combinations of MLV-VM and platinum drugs were tested against two human ovarian cancer cell lines (OVCAR-3 and CaOV-3) and on Chinese hamster ovary (CHO) cells in vitro. MLV-VM enhanced the sensitivity to cisplatin, ormaplatin and carboplatin on human ovarian carcinoma cells that show various degrees of drug sensitivity. This interaction was shown to be truly synergistic by median-effect analysis up to 90% cell kill. The combination index at 50% cell kill (Cl50) was also used to quantitate the extent of drug synergy. In the OVCAR-3 cell line, for example, the Cl50s were 0.62, 0.85 and 0.8 for cisplatin, ormaplatin and carboplatin, respectively. DNA histograms obtained by flow cytometry showed that CHO cells treated with cisplatin alone accumulated in the S-G2 segment, with a partial G2 block. The addition of 2 microM VM with cisplatin, significantly enhanced the accumulation of cells at the G2/M phase. Our results further demonstrate that in vitro treatment with VM, cisplatin and/or combination is associated with an increase in protein kinase C (PKC) activity. These findings suggest that accumulation of cells at G2/M phases and modulation of PKC activity could be among the basis for the cytotoxic synergism observed between cisplatin and VM.

Animals↗
PubMed1983

Effects of valinomycin, A23187 and repetitive sickling on irreversible sickle cell formation.

The formation of irreversibly sickled red cells has been studied by inducing cell shrinkage, ion loss, Ca2+ accumulation and membrane loss either singly or in combination. Valinomycin, A23187+Ca2+ or hypertonic saline caused shrinkage of the cells with retention of the sickled form after reoxygenation. The cells which had retained the sickle shape after treatment with the ionophores and reoxygenation remained sickled after exposure to hypotonic media. These cells were also osmotically insensitive. Retention of the sickled form was not dependent upon membrane loss as induced by repeated sickle-unsickle cycles or by A23187+Ca2+ treatment although repetitive sickling did give rise to shorter, stubbier spicules. Sickled red cells, either the endogenous irreversibly sickled cells or the sickled cells induced by deoxygenation, did not lose membrane by vesicle or spicule loss as normal cells or oxygenated sickle red cells do. Cell water loss without cell membrane loss appears to be an important factor in the irreversible sickling of red cells.

Anemia, Sickle Cell↗
PubMed1971

Freezing and melting of lipid bilayers and the mode of action of nonactin, valinomycin, and gramicidin.

An abrupt loss of effectiveness of the presumed carriers, nonactin and valinomycin, in mediating ion conductance occurred at the same temperature as the membrane fluidity, judged visually, was lost. By contrast, the effects of the presumed channel-former, gramicidin, were the same on solid and liquid membranes. Taken together, these findings imply that freezing the membrane primarily reduces the mobility of these antibiotics with little effect on their solubility.

Anti-Bacterial Agents↗
PubMed1978

Flexible valinomycin electrodes for on-line determination of intravascular and myocardial K+.

Flexible electrode systems capable of monitoring in vivo changes in venous and myocardial extracellular potassium activity were constructed using valinomycin-polyvinyl chloride matrix membrane and polyvinyl chloride tubing. Electrode impedance was 1--30 Momega, time constant 10--200 ms, drift less than 1 mV/h, and shelf life approximately 3 days (intramyocardial electrode) and approximately 6 wk (venous electrode). In vitro and in vivo accuracy were determined in 5 dogs and 18 pigs, anesthetized with sodium pentobarbital (35 mg/kg iv), with normal and elevated K+ levels. Serum and venous K+ concentration, determined using a K+ electrode with tip diameter of 1.5 mm, correlated well to serum K+ values determined by flame photometry (r = 0.997). Steady-state myocardial extracellular K+ concentration determined using double-barrel electrodes with total tip diameter of 0.6 mm also correlated well to the serum K+ concentration (r = 0.992). These electrode assemblies permit on-line, virtually instantaneous in vivo determination of intravascular and local myocardial extracellular K+ activity, a capability not previously available.

Animals↗
PubMedDate not supplied

Electrostatic potential barrier in asymmetric planar lipopolysaccharide/phospholipid bilayers probed with the valinomycin-K+ complex.

Using the carrier-ion complex valinomycin-K+, current/voltage (I/U) characteristics were registered for planar asymmetric lipid bilayers composed on one side of a phospholipid mixture and on the other side of rough mutant lipopolysaccharide. This system resembles the lipid matrix of the outer membrane of Gram-negative bacteria. The evaluation of the current/voltage curves yielded a highly asymmetric electrical potential barrier. The total potential difference between the phospholipid and the lipopolysaccharide was -85 mV, a result which cannot be explained by contributions of Gouy-Chapman potentials alone. The possible contribution of dipole potentials and influences of headgroup effects are discussed. It is shown that the asymmetry of the I/U-characteristic results from the differences of the surface charge densities of the two monolayers but not from those of the states of order of their hydrocarbon chains.

Carbohydrate Sequence↗
PubMedDate not supplied

[Effect of valinomycin on structural and functional transitions in sarcoplasmic reticulum membranes].

Effect of valinomycin (VAL) on ATPase activity and transport of calcium ions in sarcoplasmic reticulum (SR) vesicles has been studied, as well as the diffusion efflux of calcium ions from liposomes of the total fraction of SR lipids. The studies were carried out in the temperature range of 10 divided by 50 degrees. Changes in the structure of SR membranes were checked with a fluorescent probe of 3-metoxibenzantron. It was shown that at the molar ratios 1:7000-1:70 VAL decreases its ATPase activity and active transport of calcium ions in SR at all temperatures. Besides VAL decreases the rapid efflux of calcium ions from SR and the diffusion efflux of calcium ions from liposomes within the temperature range 10 degrees divided by 35 degrees; it increases the rates of these processes at higher temperatures. Simultaneously the broadening of temperature intervals of structural transitions in the SR membranes takes place.

Adenosine Triphosphatases↗
PubMed1990

Energy-linked transhydrogenase. Effects of valinomycin and nigericin on the ATP-driven transhydrogenase reaction catalyzed by reconstituted transhydrogenase-ATPase vesicles.

Reconstituted transhydrogenase-ATPase vesicles obtained with purified beef heart transhydrogenase and oligomycin-sensitive ATPase were investigated with respect to the mode of interaction between the two proton pumps, with special reference to the relative contributions of the membrane potential and proton gradient using valinomycin and nigericin in the presence of potassium. In the absence of ionophores and at low ATP concentrations, below 20 microM, the ATPase generated a proton motive force which was predominantly due to a membrane potential, whereas at saturating concentrations of ATP the proton gradient was the predominant component. The ATP-dependence of the rate of the ATP-driven transhydrogenase reaction showed apparent Km values in the low and high ATP concentration range of about 3 and 56 microM, respectively, with a corresponding difference in Vmax of about 3-fold. It is concluded that the reconstituted transhydrogenase can utilize both a membrane potential and a proton gradient, separately or combined, where the relative contributions of these components depend on the activity of the ATPase. In the reconstituted vesicles, the maximally active transhydrogenase is apparently driven by an electrochemical proton gradient where the membrane potential and the proton gradient contribute one-third and two-thirds, respectively. The rate-dependent relative generation of a membrane potential and pH gradient presumably reflects the proton pump characteristics of the ATPase and/or buffering/permeability characteristics of the vesicles rather than the properties of the transhydrogenase per se. These results are discussed in relation to current models for transhydrogenase-linked proton translocation.

Adenosine Triphosphatases↗
PubMedDate not supplied

[Relation between gramicidin D and valinomycin-induced conductivity of lipid bilayer and cholesterol levels].

Kinetics of conductance and current-voltage characteristics (VACH) were studied on the bilayer lipid membranes from egg lecithin and cholesterol modified by gramicidin D and valinomycin. There were found significant changes of ionic channels conductance g, lifetime tau and non-linearity coefficient beta of VACH of modified membranes dependent on cholesterol content. In the region of high cholesterol concentrations, more than 20 mol%, there were observed abrupt changes of the ionic channels parameters: tau increased more than ten times, conductance decreased two times and beta greater than 0 in the whole region of electrolyte concentration.

Cholesterol↗
PubMed1989

[Attempt at diagnosis of hereditary spherocytosis using the ionophore valinomycin].

On the basis of former observations that erythrocytes of patients with hereditary spherocytosis (HS) exhibit a slighter K+ efflux under the influence of valinomycin and a diminished shrinking, the attempt was made to use this phenomenon in routine diagnostics. In pair comparison the findings already known could be proved impressively. However, obligatory limiting values which make it possible to dispense with giving statements of comparison could not be established. In this report the test is of limited value for haematological diagnostics.

Erythrocytes↗
PubMed1983

Valinomycin inhibition of the electrical activity of mouse pancreatic beta-cells.

The effect of the K-ionophore valinomycin (VAL) on the electrical activity of single mouse pancreatic beta-cells was measured using the glass micro-electrode technique. In the presence of 11.1 mM glucose, after 4 min of exposure to 10 nM VAL the spike activity was abolished, bursts became irregular and after 10 min the membrane hyperpolarized 4 mV. The electrical activity was completely blocked by 100 nM VAL within 3 min and the membrane hyperpolarization averaged 10 mV. The effect of VAL was irreversible. VAL (100 nM) also inhibited the electrical activity induced by 11.1 mM glucose plus 10 mM tetraethylammonium chloride (TEA), a specific blocker of the voltage sensitive PK. Total inhibition was observed 6-7 min after VAL addition and the cell hyperpolarized 14 mV. With the simultaneous application of 10 mM TEA and 100 microM quinine, a specific blocker of the [Ca2+]i-dependent PK, in the presence of 16.7 mM glucose, the membrane showed continuous activity and progressive depolarization from -45 to -5 mV within 23 min. The subsequent addition of 100 nM VAL also hyperpolarized the cell, with the membrane potential reaching -17 mV after 7 min. On the basis of these data, we suggest that VAL affects the glucose-dependent depolarization of the beta-cell membrane by increasing K+ permeability.

Animals↗
PubMedDate not supplied

[Effect of ionophores A 23187 and valinomycin on acetyocholinesterase activity in rabbit erythrocytes].

Activity of cholinesterase was higher in young erythrocytes when the cell populations of various age were studied; the enzymatic activity was increased after addition of valinomycine into a medium independently on the antibiotic concentration and the enzyme activation was more pronounced in the old population of erythrocytes. The same alterations were observed in presence of calcium ionophore A 23187 and nystatin. Alterations in the enzymatic activity appear to depend on changes of erythrocyte membrane properties in ageing as well as on introduction of ionophore into the membrane.

Animals↗
PubMed1981

Red cell response to A23187 and valinomycine in Duchenne muscular dystrophy.

Treatment of red cells from Duchenne muscular dystrophy (DMD) patients with A23187 induced identical responses with those in controls in terms of Ca++ flux, shrinkage, ATP depletion, hypotonic lysis protection, and glycolysis stimulation. The level of RC-free calcium seemed not to be altered in DMD. Valinomycine-induced shrinkage was enhanced significantly in DMD red blood cells.

Anti-Bacterial Agents↗
PubMed1982

[Effect of valinomycin and nonactin on monovalent cation transport in mitochondria].

Unidirectional fluxes of tracers 137Cs+ (+valinomycin) and 204Tl+ (+nonactin) in mitochondria maintained under stationary state at 0 degree C have been studied. The tracer uptake in energized mitochondria (Q infinity Cmit/Cmed = Kin/kout) was about 10 times as high compared to that in a deenergized state. Energization caused a 5-10 fold increases of the influx rate constant kin, while the efflux rate constant, kout, decreased only by 1.5-2 times of less. There was a positive correlation between Q infinity and kin. No correlation could be found between Q infinity and kout. The results obtained suggest that under the experimental conditions studied the energization did not increase substantially the membrane potential expected to retard the efflux of permeant cations. In the presence of ionophores the monovalent cations are supposed to be accumulated in mitochondria against the electrochemical gradient.

Animals↗
PubMed1982

Steady-state fluorescence polarization in planar lipid membranes. Experimental and theoretical analysis of the fluorophores 8-anilino-1-naphthalenesulfonate, 1,6-Diphenyl-1,3,5-hexatriene, dansyllysine-valinomycin and n-(9-anthroyloxy) fatty acids.

In continuation of earlier work, the steady-state fluorescence polarization in a globally oriented system of planar lipid membranes was analyzed experimentally and theoretically for the fluorophores 8-anilino-1-naphthalenesulfonate, 1,6-diphenyl-1,3, 5-hexatriene, dansyllysine-valinomycin and n-(9-anthroyloxy) fatty acids. The theoretical analyses of experiments were mainly done in terms of the mean orientation of transition moments with respect to the membrane normal, an angle describing the region of hindered rotational diffusion and the coefficients of rotational diffusion perpendicular to the membrane and around the membrane normal. The nonvanishing angle between the moments of absorption and emission was taken into account. In the case of n-(9-anthroyloxy) fatty acids it was found that the orientational disorder increases significantly with the depth of the fluorophore within the membrane. In order to compare with recent results from time-dependent fluorescent polarization in globally isotropic membrane suspensions and with 2H-NMR experiments, the second moment ('order parameter') of the steady-state orientational distribution of absorption dipoles was calculated. For all fluorophores the theoretical analysis indicates a preferred orientation of absorption moments within the membrane plane.

Journal Article↗
PubMed1999

A General Methodology for Automated Solid-Phase Synthesis of Depsides and Depsipeptides. Preparation of a Valinomycin Analogue.

A general methodology is described that allows the solid-phase synthesis of depsides and depsipeptides from chiral alpha-hydroxy- and alpha-amino acids. The results of studies with different protecting groups for the alpha-hydroxy acids and coupling systems for depside bond formation are presented. The oligomers were prepared using a Wang-type linker with final TFA/CH(2)Cl(2) cleavage. Depside linkage of the THP-protected acids (THP = tetrahydropyranyl) to the resin-bound chains was achieved with DIC/DMAP (DIC = diisopropylcarbodiimide, DMAP = 4-(dimethylamino)pyridine) and monitored by a color test with 4-(p-nitrobenzyl)pyridine. THP deprotection was achieved with p-TsOH in CH(2)Cl(2)/MeOH and was monitored by GC. Following the established procedure, depsides made up from the same enantiomer (i.e., H-[L-Man](8)-OH, 25), by both enantiomers (i.e., H-[D-Man-L-Man](4)-OH, 26), or by different hydroxy acids in the same chain (i.e., H-[L-Lac-L-Hiv](3)-OH, 27) were prepared with an average yield of 95-97% per cycle. The linear precursor of the valinomycin analogue 30 ([L-Val-D-Man-D-Val-L-Lac](3)) was entirely synthesized on resin and cyclized in solution. Cyclization of the open-chain depsides is the final step in the preparation of a new class of chiral alpha-hydroxyester macrocycles.

Journal Article↗
PubMed1967

The effect of valinomycin on potassium and sodium permeability of HK and LK sheep red cells.

A cyclic depsipeptide antibiotic, valinomycin, was found to produce increased selective permeability of the plasma membranes of HK and LK sheep red blood cells to potassium but not to sodium ions. The compound had relatively little effect on the active extrusion of sodium from HK sheep red blood cells or on the Na + K-stimulated ATPase activity of membranes derived from these cells. It is proposed that the selective cation permeability produced by this compound depends primarily on steric factors, particularly the relationship between the diameter of the ring and the effective diameter of the ion. The significance of these results for the problem of the mechanism of ionic selectivity in natural membranes is discussed.

Adenosine Triphosphatases↗