valinomycin and nonactin

We describe the phenomenon of mechanoelectrical transduction in macroscopic lipid bilayer membranes modified by two cation-selective ionophores, valinomycin and nonactin. We found that bulging these membranes, while maintaining the membrane tension constant, produced a marked supralinear increase in specific carrier-mediated conductance. Analyses of the mechanisms involved in mechanoelectrical transduction induced by the imposition of a hydrostatic pressure gradient or by an amphipathic compound chlorpromazine reveal similar changes in the charge carrier motility and carrier reaction rates at the interface(s). Furthermore, the relative change in membrane conductance was independent of membrane diameter, but was directly proportional to the square of membrane curvature, thus relating the observed phenomena to the bilayer bending energy. Extrapolated to biological membranes, these findings indicate that ion transport in cells can be influenced simply by changing shape of the membrane, without a change in membrane tension.

Topics: Anti-Bacterial Agents; Biological Transport, Active; Cations, Monovalent; Cell Membrane Permeability; Chlorpromazine; Electric Conductivity; Hydrostatic Pressure; Iontophoresis; Kinetics; Lipid Bilayers; Macrolides; Mathematics; Membrane Potentials; Models, Biological; Thermodynamics; Valinomycin

The effects of several K(+)-selective neutral ionophores on membrane electrical characteristics of differentiated NG108-15 (neuroblastoma X glioma hybrid) cells were examined. Specifically, alterations in membrane resting potential (V(m)), input resistance (R(in)) and electrically-induced action potential generation were determined upon bath application of enniatin (0.1-10 microg/ml), nonactin (0. 1-10 microM) and valinomycin (0.1-10 microM). Although some cells exhibited a slight hyperpolarization and/or reduced R(in), i.e. membrane electrical correlates of enhanced K(+) loss, neither V(m) nor R(in) were significantly altered by any of the ionophores. However, valinomycin and especially nonactin affected action potentials induced by electrical stimulation. This was apparent in the ablation of action potentials in some cells and in the occurrence of degenerative changes in action potential shape in others. The simultaneous administration of the neutral ionophores and the protonophore CCCP or the superfusion of enniatin, nonactin or valinomycin in high (50 mM) glucose-containing physiological solution did not yield more extensive alterations in V(m) or R(in). These data suggest that the neutral ionophores are unable to materially enhance K(+) flux above the relatively high resting level in NG108-15 cells. Thus, alterations in action potentials appear to be unrelated to K(+) transport activity.

Topics: Action Potentials; Analysis of Variance; Animals; Anti-Bacterial Agents; Cell Membrane; Depsipeptides; Dose-Response Relationship, Drug; Electric Stimulation; Glioma; Gramicidin; Hybrid Cells; Ion Transport; Ionophores; Macrolides; Membrane Potentials; Mice; Neuroblastoma; Neurons; Nigericin; Peptides; Potassium; Rats; Tumor Cells, Cultured; Valinomycin

A variety of neutral carrier type ionophores for monovalent cations were employed to prepare solid-state cation-selective electrodes (SSEs) for use as a detector in single-column ion chromatography (IC). The polyurethane-based pseudoreference electrode made it possible to assemble an array type SSE detector for IC. An SSE-based detector provides not only the overall chromatogram for the separated ion species (monensin methyl ester-nonactin-based membrane), but also the enhanced chromatogram for specified ions of interest (valinomycin as K+ and nonactin for NH4+). This feature makes it possible to perform highly quantitative analysis with low detection limits even if the separation efficiency of the ion-exchange is not sufficient. Since SSE-based IC detectors are easily miniaturized and replaceable at low cost, they are an ideal component of a portable IC system.

Topics: Cations, Monovalent; Chromatography, Ion Exchange; Electrodes; Lithium; Macrolides; Potassium; Quaternary Ammonium Compounds; Sodium; Valinomycin; Water

Recently, a gastric Mg(2+)-ATP-dependent phospholipid flippase was found. Here, the effects of ionophores and monovalent cations on the gastric flippase were examined. We found that translocation of the fluorescent analogue of phosphatidylcholine was inhibited by valinomycin in the presence of K(+). The inhibition depended on both the concentrations of valinomycin and K(+). Valinomycin did not inhibit translocation in the absence of K(+). Protonophores, carbonylcyanide-m-chlorophenylhydrazone (CCCP) and carbonylcyanide-p-(trifluoromethoxy)phenylhydrazone (FCCP), accelerated translocation by 190-270%. These increases were completely abolished by 2-methyl-8-(phenylmethoxy)imidazo-[1, 2-a]pyridine-3-acetonitrile (SCH 28080), a gastric flippase inhibitor. Since these protonophores did not affect the Mg(2+)-dependent ATPase activity that is responsible for phospholipid translocation by the flippase, the coupling ratio of the amount of transported phospholipids/the amount of hydrolyzed ATP was variable and seemed to depend on the state of the membrane bilayer, for example fluidity. Inhibition by the valinomycin-K(+) complex was abolished in the presence of CCCP or FCCP, indicating the valinomycin-K(+)-CCCP(FCCF) ternary complex did not inhibit the flippase.

Topics: 4-Chloro-7-nitrobenzofurazan; Animals; Anti-Bacterial Agents; Biological Transport; Ca(2+) Mg(2+)-ATPase; Carbonyl Cyanide m-Chlorophenyl Hydrazone; Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; Enzyme Activation; Gastric Mucosa; Gramicidin; Intracellular Membranes; Ionophores; Macrolides; Phosphatidylcholines; Potassium Chloride; Sodium Chloride; Swine; Valinomycin

Streaming potentials have been measured for gramicidin channels with a new method employing ion-selective microelectrodes. It is shown that ideally ion-selective electrodes placed at the membrane surface record the true streaming potential. Using this method for ion concentrations below 100 mM, approximately seven water molecules are transported whenever a sodium, potassium, or cesium ion, passes through the channel. This new method confirms earlier measurements (Rosenberg, P.A., and A. Finkelstein. 1978. Interaction of ions and water in gramicidin A channels. J. Gen. Physiol. 72:327-340) in which the streaming potentials were calculated as the difference between electrical potentials measured in the presence of gramicidin and in the presence of the ion carriers valinomycin and nonactin.

Topics: Anti-Bacterial Agents; Electrochemistry; Gramicidin; Ion Channels; Macrolides; Membrane Potentials; Microelectrodes; Models, Biological; Valinomycin

The decrease of the intracellular concentration of drug in resistant cells compared to sensitive cells is, in most cases, correlated with the presence, in the membrane of resistant cells, of a 170-kDa P-glycoprotein responsible for an active efflux of the drug. In an attempt to identify mechanism(s) by which multidrug resistance can be circumvented, we have examined the cellular accumulation of 4'-O-tetrahydropyranyl-adriamycin, alone and in conjunction with various ionophores on the one hand and with cyclosporin A on the other hand. The present study was performed using a spectrofluorometric method with which it is possible to follow continuously the uptake and release of fluorescent molecules by living cells, as the incubation of the cells with the drug proceeds. Erythroleukemia K562 cell lines were used. Using experimental conditions in which these ionophores were unable to modify either the intracellular pH, or the transmembrane potential, or to induce an intracellular ATP depletion, we have shown that mobile ionophores as well as cyclosporin inhibit the P-glycoprotein-mediated efflux of 4'-O-tetrahydropyranyl-adriamycin in K562 resistant cells, whereas gramicidin, a channel-forming ionophore, does not. The concentration that must be used to inhibit 50% of the efflux was 0.7 microM for valinomycin, 0.4 microM for nonactin, 0.2 microM for nigericin, 1.1 microM for monensin, 0.4 microM for lasalocid, 1.2 microM for calcimycin and 0.4 microM for cyclosporin. Due to the high toxicity of the ionophores, the observation that they increased 4'-O-tetrahydropyranyl-adriamycin accumulation in the multidrug-resistant cells is not correlated with an effect of these compounds on drug resistance. However, the correlation exists in the case of cyclosporin. From our data showing that lipophilic neutral complexes, formed between carboxylic ionophores and metal ions, are both able to inhibit the P-glycoprotein-mediated efflux of anthracycline we can infer that the lipophilicity but not the cationic charge is an important physical property.

Topics: Adenosine Triphosphate; Anti-Bacterial Agents; Antibiotics, Antineoplastic; ATP Binding Cassette Transporter, Subfamily B, Member 1; Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; Carrier Proteins; Cell Division; Cyclosporine; Doxorubicin; Drug Resistance; Gramicidin; Humans; Ionophores; Macrolides; Membrane Glycoproteins; Membrane Potentials; Tumor Cells, Cultured; Valinomycin

Apoptosis of murine thymocytes induced by either methylprednisolone or valinomycin was studied by flow cytometry. The apoptosis induced by methylprednisolone followed three stages: an initial decrease in cell volume, indicated by a fall in forward scatter accompanied by faint ethidium bromide staining, a second stage in which the cells became brightly stained by ethidium bromide, and a final stage when the cells were apparently less fluorescent as the nuclei disintegrated into apoptotic bodies. As the forward scatter of cells decreased there was a simultaneous depolarization of the cells and an elevation of intracellular calcium. These early changes preceded the fragmentation of the DNA which also preceded the intense staining of the cells by ethidium bromide. Methylprednisolone-induced apoptosis was inhibited by low concentrations (1 x 10(-7) M) of valinomycin and nonactin, neither of which could themselves induce apoptosis at these low concentrations. Cadmidazolium and cycloheximide arrested the program at an early stage. Okadaic acid allowed volume loss and ethidium bromide staining to proceed in the absence of DNA fragmentation. At high concentrations (1 x 10(-5) M) valinomycin induced a form of apoptosis, but nonactin only caused the cells to fragment. The valinomycin-induced apoptosis, although it involved the degradation of DNA and the disintegration of the nuclei into apoptotic bodies, differed from the methylprednisolone apoptosis as it did not involve a decrease of cell volume and was not inhibited by cycloheximide or affected by okadaic acid.

Topics: Animals; Anti-Bacterial Agents; Apoptosis; Cells, Cultured; Cycloheximide; DNA Damage; Ethers, Cyclic; Flow Cytometry; Imidazoles; In Vitro Techniques; Macrolides; Male; Methylprednisolone; Mice; Okadaic Acid; Thymus Gland; Valinomycin

The development and application of model membrane systems on the basis of tetraether lipids from Thermoplasma acidophilum has been proposed. In this respect incorporation of membrane proteins and ionophores is indispensable and is demonstrated in the case of alamethicin, melittin, nonactin, and valinomycin by calorimetry. Dipalmitoylphosphatidylcholine (DPPC) and dihexadecylmaltosylglycerol (DHMG) were chosen for comparison. Melittin and alamethicin prove to broaden the lipid phase transition and to reduce the melting temperature Tm and enthalpy change (delta H) of the main phospholipid from T. acidophilum (MPL) and DPPC. The decrease in Tm, however, is more pronounced in DPPC than in MPL. Valinomycin shows only a marginal effect on the temperature and width of the transition; delta H is reduced in MPL and remains constant in DPPC and DHMG. With nonactin the phase transition of DPPC is quenched, and delta H and the half-height width are increased. DHMG is affected to a lesser extent and MPL only marginally. The four ionophores exhibit different modulation of the phase transition behavior of the various lipids as expected from their varying molecular structures. Thus, the integral membrane protein alamethicin, the peripheral protein melittin, valinomycin, and nonactin interact primarily with lipid head groups and are readily incorporated into the tetraether lipid structures.

Topics: 1,2-Dipalmitoylphosphatidylcholine; Alamethicin; Amino Acid Sequence; Anti-Bacterial Agents; Calorimetry, Differential Scanning; Glyceryl Ethers; Macrolides; Melitten; Models, Biological; Molecular Sequence Data; Phospholipid Ethers; Thermoplasma; Valinomycin

To investigate the effect of ionophores on Cl- distribution in human erythrocyte suspensions, we measured the membrane potential by using 19F and 31P NMR methods. Incubation of human erythrocytes with 0.005 mM of the neutral ionophores valinomycin and nonactin resulted in membrane potentials of -21.2 and -17.8 mV in the presence and absence of DIDS. However, 0.020 mM of the carboxylic ionophores lasalocid, monensin, and nigericin yielded membrane potentials similar to those measured in the absence of ionophore (-9.4 mV). In methanol, the 35Cl- NMR linewidth in the presence of valinomycin was twice as broad as those observed in the presence of carboxylic ionophores, suggesting that neutral ionophores induce Cl- efflux in part via ion pairing.

Topics: 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Anti-Bacterial Agents; Chlorides; Erythrocyte Membrane; Erythrocytes; Humans; In Vitro Techniques; Ionophores; Kinetics; Lasalocid; Macrolides; Magnetic Resonance Spectroscopy; Membrane Potentials; Monensin; Nigericin; Valinomycin

Two ionophores specific for K+, valinomycin and beauvericin, induce a type of cell death very similar to apoptosis due to tumor necrosis factor (TNF alpha). Both ionophores cause cytolysis accompanied by internucleosomal DNA fragmentation of the dying cell into units of 200 base pairs. Morphologically, the cell death appears to consist of a mixture of nuclear apoptotic changes and cytoplasmic necrotic changes. As in the case for TNF alpha-mediated death, metabolic inhibitors have no effect on the course of cell death, but DNA fragmentation and cytolysis are decreased by the endonuclease inhibitor, zinc. Beauvericin and valinomycin trigger an increase in the cytoplasmic calcium concentration, most likely due to release of calcium from intracellular stores, and chelation of cytoplasmic calcium with quin-2 inhibits DNA fragmentation. Thus, these ionophores set off apoptosis through a calcium-activatable endonuclease, suggesting that other nonphysiological toxins might also cause apoptosis through their ability to indirectly elevate the cytoplasmic calcium concentration, without the need to invoke specific surface receptors.

Topics: Animals; Anti-Bacterial Agents; Calcium; Cell Death; Depsipeptides; DNA; Ionomycin; Ionophores; Macrolides; Mice; Microscopy, Electron; Nigericin; Peptides; Peptides, Cyclic; Tumor Cells, Cultured; Valinomycin

The K(+)-ionophores valinomycin and nonactin induce a qualitatively identical change of the visible spectrum of isolated oxidized cytochrome c oxidase (red shift), but the amplitude is half with nonactin. Valinomycin, in the presence or absence of a protonophore, stimulates the respiration of the reconstituted enzyme to a higher extent than nonactin and results in a higher Km for cytochrome c. In contrast, nonactin causes a fivefold rate of proton conductivity across a liposomal membrane, after induction of a K(+)-diffusion potential. The data indicate that respiratory control by these antibiotics is not only due to degradation of a membrane potential, but rather to specific interaction with and modification of cytochrome c oxidase.

Topics: Animals; Anti-Bacterial Agents; Electron Transport Complex IV; In Vitro Techniques; Ionophores; Kinetics; Liposomes; Macrolides; Oxygen Consumption; Potassium; Protons; Spectrophotometry; Valinomycin

The adsorption of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) as well as of other dipolar molecules to the interface of artificial lipid membranes gives rise to a change of the dipole potential between the membrane interior and water. As a consequence of the adsorption of the neutral species, the conductance of planar membranes, observed in the presence of the macrocyclic ion carriers nonactin or valinomycin, may change by many orders of magnitude. Using this effect in combination with a laser-T-jump technique, the kinetics of the adsorption process were measured and were interpreted on the basis of a Langmuir-isotherm. A partition coefficient (at small concentrations) of beta HA = 4.7 x 10(-4) cm, a rate constant of desorption kHA greater than or equal to 100 s-1 and a maximum surface density ND = 7.7 x 10(13)/cm2 were found. The concentration at half saturation is KHA = 2.7 x 10(-4) M. Using these values the membrane conductance induced by the ion carrier nonactin and the shape of the current-voltage relationship as a function of the ligand concentration in water was analyzed. A maximum dipole potential of VDmax = -239 mV and a contribution of b = 3.1 x 10(-15) V cm2 per single adsorbed 2,4-D molecule was found. 74% of the dipole potential acts on the inner membrane barrier separating the two interfacial adsorption planes of nonactin. The remainder (26%) favours interfacial complex formation between nonactin and K+ from the aqueous phase. The data hold for membranes formed from dioleoyllecithin in n-decane.

Topics: 2,4-Dichlorophenoxyacetic Acid; Adsorption; Anti-Bacterial Agents; Lasers; Macrolides; Mathematics; Membrane Potentials; Membranes, Artificial; Models, Biological; Phloretin; Valinomycin

The interactions of carrier ionophores, nonactin, A23187, and lasalocid A with liposomes formed from the synthetic lipids dimyristoylphosphatidylcholine and dipalmitoylphosphatidylcholine are investigated by differential scanning calorimetry and 1H and 31P nuclear magnetic resonance techniques. The results indicate that the mode of interaction of these ionophores is dependent on the fluidity of the bilayer and on the chemical nature of these ionophores. The 31P NMR studies are suggestive of the formation of small particles that are probably intervesicular lipid-ionophore aggregates in multilamellar vesicles when they are incorporated with these ionophores at high concentrations. The results are interpreted on the basis of the chemical structure and conformations of the ionophores in membrane mimetic media. The 1H NMR line-width measurements indicate that the aromatic rings containing the carboxyl groups of lasalocid A and A23187 are located near the membrane interface while the rest of the molecule is buried in the membrane interior.

Topics: 1,2-Dipalmitoylphosphatidylcholine; Anti-Bacterial Agents; Calcimycin; Calorimetry, Differential Scanning; Dimyristoylphosphatidylcholine; Lasalocid; Lipid Bilayers; Macrolides; Magnetic Resonance Spectroscopy; Membrane Fluidity; Models, Biological; Molecular Conformation; Valinomycin

Planar lipid membranes in the presence of the ion carriers valinomycin or nonactin were irradiated with 14 MeV electrons from a linear accelerator. A large increase of the membrane conductance by up to more than two orders of magnitude was found. The effect is virtually abolished either at high pH, or in the absence of oxygen, or in the presence of the radical scavenger ethanol. A further prerequisite for the effect is the presence of unsaturated fatty acid residues. A kinetic analysis of the carrier transport model based on current-voltage curves and on voltage-jump relaxation experiments was performed as a function of radiation dose. Only the translocation rate constant, kMS, of the charged carrier-ion complex was found to be influenced by irradiation. The effect is interpreted as an increase of the polarity (dielectric constant) of the membrane interior induced by the presence of polar products of lipid peroxidation. A combined action of OH- and HO2-radicals seems to be responsible for the phenomena. At large radiation doses (greater than or equal to 10(3) Gy) a reduction of the membrane conductance was observed. This is interpreted as an increased microviscosity, possibly caused by cross-linking of fatty acid residues. Ion carriers represent sensitive probes of radiation induced membrane damage.

Topics: Anti-Bacterial Agents; Biological Transport; Electric Conductivity; Free Radicals; Hydrogen-Ion Concentration; Lipid Bilayers; Lipid Peroxides; Macrolides; Membrane Lipids; Membrane Potentials; Oxygen; Phosphatidylcholines; Valinomycin; Viscosity

The effects of 10(-7) M valinomycin, nonactin, and monactin on human erythrocytes, frog sartorius muscle, and frog ovarian oocytes in the presence of varying external K+ concentration were studied. The results showed essentially a consistent but relatively modest increase of the K+ permeability constant in cm/sec with all three antibiotics on human erythrocytes. No change in response to any one of the antibiotics was observed in frog muscles or in frog ovarian eggs. These results and reports of similar failure to demonstrate ionophore-mediated increase of K+ permeability in squid axon and inner membrane of the liver mitochondria led to the conclusion that lipid membrane barrier to ionic traffic may be significant in the human erythrocytes but even here one must regard the evidence as tentative. In contrast, for the majority of other cell types studied, the data indicate the primary, if not exclusive route of ion traffic, is via the nonlipid component of the cell membrane. The evidence that these nonlipid paths are the fixed charge-polarized water layer complex and that they cover much of the cell surface of many types of living cells was discussed.

Topics: Animals; Anti-Bacterial Agents; Body Water; Erythrocytes; Humans; Ionophores; Lipid Bilayers; Macrolides; Muscles; Ovum; Potassium; Rana pipiens; Valinomycin

Zymogen granules from rat pancreas were prepared on a 40% Percoll gradient at free calcium levels less than 0.2 microM. We have previously shown [Am. J. Physiol. 246 (Gastrointest. Liver Physiol. 9)] that zymogen granules prepared by this method are stable in vitro for more than 1 h in "physiological buffers." The electrolyte permeabilities of the zymogen granule membrane were investigated to determine the basis for this stability. Ionic permeabilities were estimated from rates of osmotic lysis and measured as decrease in optical density (OD) of granule suspensions. OD correlated linearly with lysis, as indicated by release of amylase, except for the highest and lowest 10% of the OD of intact granules. Lysis of freshly isolated granules was slow in Na+ or K+ salt solutions (e.g., t1/2 approximately 3 h for Cl-) but was accelerated 5- to 50-fold when cation ionophores were present simultaneously. This behavior indicates that zymogen granules have low endogenous permeabilities to the cations Na+ and K+, but are highly permeable to a variety of anions. Both anion conductance and anion-exchange pathways were found. The relative selectivity of the anion conductance pathway was SCN- greater than Br- approximately NO-3 greater than SO2-(4) greater than acetate- approximately Cl- greater than isethionate-. The relative selectivity sequence for anion/-OH- exchange was acetate- greater than SCN- greater than Br- approximately NO-3 approximately Cl- much greater than isethionate- greater than SO2-(4). The anion transport blocker DIDS blocked the electrogenic pathway with a half-maximal effectiveness at approximately 2 microM. DIDS had little effect on the anion-exchange pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Animals; Anti-Bacterial Agents; Cell Membrane Permeability; Cytoplasmic Granules; Electrolytes; Enzyme Precursors; Macrolides; Male; Mathematics; Models, Biological; Nigericin; Pancreas; Rats; Rats, Inbred Strains; Valinomycin

We recorded high-resolution 13C NMR spectra of the macrocyclic antibiotic ionophores valinomycin, nonactin, and tetranactin in the solid state by the cross-polarization-magic angle spinning (CP-MAS) method, in order to gain insight into the use of conformation-dependent 13C chemical shifts as a convenient means to delineate a conformational change induced by metal ion complexation. The 13C peak splittings in the solid state are consistent with the symmetry properties of the ionophores as revealed by X-ray diffraction: C2 symmetry in free tetranactin and S4 or S6 symmetry for a variety of metal complexes of nonactin and tetranactin or the K+ complex of valinomycin, respectively. Interestingly, many of the 13C NMR peaks of carbons in the skeletal backbones were significantly displaced (up to 8 ppm). The displacements of the peaks were explained by a conformational change as characterized by variations of torsion angles. Accordingly, we were able to obtain conformational features of Na+ and Cs+ complexes of valinomycin, for which X-ray diffraction data are unavailable, on the basis of the displacements of the 13C NMR peaks. Further, we discuss conformational features of these complexes in chloroform solution, with reference to those observed in the solid state.

Topics: Anti-Bacterial Agents; Carbon Isotopes; Cesium; Ionophores; Macrolides; Magnetic Resonance Spectroscopy; Molecular Conformation; Potassium; Pyrans; Sodium; Solutions; Valinomycin

The interaction between bepridil and mitochondrial cytochrome c oxidase has been studied using the purified enzyme either in aqueous suspensions in the presence of detergents, or embedded into phospholipid vesicles. The investigation, systematically extended to nonactin and valinomycin for comparison, showed that: (a) valinomycin and nonactin induce similar changes in the visible absorption spectrum of cytochrome oxidase; these changes are quite different from those induced by bepridil. (b) The three compounds have an effect on the functional properties of purified, solubilized oxidase which may be related to binding. In particular, bepridil displays a complex pH-dependent effect which at concentrations below 50 microM results in a stimulation of the activity of approximately 30% starting with the oxidized resting enzyme. At variance with valinomycin and nonactin, the stimulatory effect is the same, within the errors, for the detergent-suspended, the vesicle-embedded and even the Keilin-Hartree particles. (c) In the case of detergent-suspended oxidase, the stimulatory effect of bepridil is also similar whether the enzyme is in the resting or in the pulsed state. If the oxidase is embedded into vesicles, however, the pulsed state is significantly more sensitive to bepridil than the resting one. These results are discussed in the light of the possible role assigned to pulsed oxidase in the regulation of the electron flux through the respiratory chain.

Topics: Animals; Anti-Bacterial Agents; Bepridil; Cattle; Electron Transport Complex IV; Liposomes; Macrolides; Mitochondria, Heart; Pyrrolidines; Solutions; Spectrophotometry; Valinomycin

A new electroanalytical method of voltamperometry at the interface of two immiscible electrolyte solutions (ITIES) is based on electrochemical polarization of a liquid/liquid interface. The resulting current voltage characteristics completely resemble those obtained with metallic electrodes. The charge transfer processes are either the direct ion transfer across the ITIES or the transfer facilitated by macrocyclic ionophores. Determination of tetracycline antibiotics is based on the direct transfer of the cationic forms of these substances in acid media. Determination of valinomycin, nonactin and monensin acting as ion carriers is connected with the facilitated alkali metal ion transfer. In general, antibiotic concentrations higher than 0.02-0.05 mmol/l can be determined with this method. Monensin can also be determined in the extracts of Streptomyces cinnamonensis.

Topics: Anti-Bacterial Agents; Electrochemistry; Ion Exchange; Ionophores; Macrolides; Monensin; Nitrobenzenes; Tetracyclines; Valinomycin; Water

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.

Topics: Animals; Anti-Bacterial Agents; Biological Transport; Cations, Monovalent; Cesium Radioisotopes; Energy Metabolism; Kinetics; Macrolides; Mitochondria, Liver; Radioisotopes; Rats; Thallium; Valinomycin

Topics: Anti-Bacterial Agents; Cesium; Macrolides; Membrane Potentials; Mitochondria; Onium Compounds; Rotenone; Rubidium; Succinates; Thallium; Trityl Compounds; Valinomycin