2-(dimethylaminostyryl)-1-ethylpyridinium and tetraphenylphosphonium

The mechanism of uptake of the fluorescent dye 2-(4-dimethylaminostyryl)-1-ethylpyridinium cation (DMP+) into cells and vesicles of the acrA strain AS-1 of Escherichia coli was examined. Uptake was energized by substrate oxidation and discharged by uncouplers. Uptake was enhanced by the presence of tetraphenylphosphonium cation, tetraphenylboron anion and tributyltin chloride, which may inhibit the efflux system for DMP+. Uptake was inhibited by 5-methoxyindole-2-carboxylic acid (MIC). By the use of ionophores with right-side-out vesicles loaded with monovalent cations it was shown that DMP+ uptake could be driven both by the establishment of a membrane potential across the vesicle membrane and by a H+/DMP+ antiport system. Attempts to demonstrate the latter mechanism in everted membrane vesicles were unsuccessful.

Topics: Animals; Cations; Cell Membrane Permeability; Electrophysiology; Energy Metabolism; Escherichia coli; Fluorescent Dyes; Indoles; Mitochondria, Liver; Nigericin; Onium Compounds; Organophosphorus Compounds; Pyridinium Compounds; Rats; Tetraphenylborate; Trialkyltin Compounds; Valinomycin

At pH 7, addition of glucose under anaerobic conditions to a suspension of the yeast Saccharomyces cerevisiae causes both a transient hyperpolarization and a transient net efflux of K+ from the cells. Hyperpolarization shows a peak at about 3 min and a net K+ efflux at 4-5 min. An additional transient hyperpolarization and net K+ efflux are found after 60-80 and 100 min, respectively. Addition of 2-deoxyglucose instead of glucose does not lead to hyperpolarization of the cells or K+ efflux. At low pH, neither transient hyperpolarization nor a transient K+ efflux are found. With ethanol as substrate and applying aerobic conditions, both a transient hyperpolarization and a transient K+ efflux are found at pH 7. The fluorescent probe 2-(dimethylaminostyryl)-1-ethylpyridinium appears to be useful for probing changes in the membrane potential of S. cerevisiae. It is hypothesized that the hyperpolarization of the cells is due to opening of K+ channels in the plasma membrane. Accordingly, the hyperpolarization of the cells at pH 7 is almost completely abolished by 1.25 mM K+, whereas the same amount of Na+ does not reduce the hyperpolarization.

Topics: Cell Membrane; Cell Membrane Permeability; Deoxyglucose; Ethanol; Fluorescent Dyes; Glucose; Hydrogen-Ion Concentration; Kinetics; Mathematics; Membrane Potentials; Onium Compounds; Organophosphorus Compounds; Potassium; Potassium Channels; Pyridinium Compounds; Saccharomyces cerevisiae; Sodium; Spectrometry, Fluorescence

The extent of accumulation of methyltriphenylphosphonium ion by Escherichia coli was shown to be dependent on the permeability of the outer membrane and the activity of an efflux system for this compound. Evidence consistent with the operation of a single efflux system for compounds such as phosphonium ions, phenanthridiniums and flavines is presented. Studies on the energy coupling mechanism for this efflux system indicated that it was driven by the transmembrane proton electrochemical gradient.

Topics: Energy Metabolism; Escherichia coli; Ethidium; Free Radicals; Membrane Potentials; Onium Compounds; Organophosphorus Compounds; Pyridinium Compounds; Trityl Compounds