Interaction of ethidium bromide with yeast cells investigated by electron probe X-ray microanalysis

Potassium ion efflux induced by cationic compounds in yeast

Potassium efflux in yeast induced by several cationic compounds showed different characteristics. All of the observed efflux required glucose as substrate at the concentrations used. For most of them, the phenomenon required binding of the cationic compound to the cell surface and increased with the negative cell surface charge, and for all the compounds tested, it depended on a metabolizable substrate. Efflux induced with terbium chloride appeared more likely due to the function of a K+/H+ antiporter. With DEAE-dextran and dihydrostreptomycin, potassium efflux was dependent on the cell potassium content and was also sensitive to osmotic changes of the medium. DEAE-dextran-provoked efflux was not due to cell disruption. Dihydrostreptomycin seemed to activate a potassium efflux system which could not be studied in isolation, but its inhibition of potassium uptake may also be involved. Except for cells treated with ethidium bromide, no appreciable cell disruption was observed. The potassium efflux observed appears to be a membrane phenomenon reversible after washing with magnesium chloride.

Photodynamic treatment of yeast cells with the dye toluidine blue: all-or-none loss of plasma membrane barrier properties

Photodynamic treatment of Kluyveromyces marxianus with the sensitizer Toluidine blue leads to the loss of colony forming capacity. In this paper, the influence of this treatment on the barrier properties of the plasma membrane has been studied. Photodynamic treatment with the dye Toluidine blue resulted in efflux of potassium ions and E260-absorbing material. Moreover, cells became stainable with erythrosine. It is concluded that the permeability change induced by photodynamic treatment proceeds in an all-or-none fashion. Treatment of this yeast strain, with the dye and light, also induced a diminution of the cell volume. This process is most likely not coupled to the cellular potassium content, but rather to the integrity of the vacuole. These data suggest that the vacuole has an important function in the maintenance of cell volume. Finally, it was observed that the loss of cell viability was not induced by the all-or-none loss of barrier properties.

An energy-dependent efflux system for potassium ions in yeast

An efflux of potassium ions was demonstrated in mutants of yeast cells lacking a functional high affinity carrier system for monovalent cations. This efflux showed the following characteristics: (a) It was stimulated by the presence of a substrate, either glucose or ethanol. (b) It was stimulated by several cationic organic molecules, such as ethidium bromide, dihydrostreptomycin, diethylaminoethyldextran, and also by trivalent cations, such as Al3+ and lanthanides; this stimulation also depended on the presence of a substrate. (c) K+ efflux was decreased in yeast mutants with decreased ATPase activity, which generated a lower membrane potential. (d) Although the efflux appeared to be of an electrogenic nature, producing hyperpolarization of cells, it was accompanied by the efflux of phosphate, probably as an anion partially compensating for the large amount of cations leaving the cell. (e) K+ efflux was also accompanied by an uptake of protons. (f) The efflux appeared more clearly in cells grown in YPD medium, and not in more complex media nor in the same YPD medium if supplemented with Ca2+ or Mg2+. Efflux of monovalent cations produced by Tb3+ and organic cationic agents was also demonstrated in wild type strains. This efflux system appears to be, at least partially, electrogenic, but seems to be also an exchange system for protons and to function as a symport with phosphate; it may be involved in the regulation of the internal pH of the cell, and appears to be regulated by its link to the energetic status of the cell, probably through the membrane potential.

Simulation of all-or-none K+ efflux from yeast provoked by xenobiotics

In experiments dealing with the effect of xenobiotics upon the efflux of K+ from yeast cells, one should be aware that when this efflux proceeds via an all-or-none process, the K+ being released from the intoxicated cells can again be accumulated into the still unaffected cells. Therefore, the measured net efflux of K+ will be less than the efflux from the intoxicated cells. The difference between these two magnitudes can be minimalized by incubating the cells for only a short period and on applying yeast densities that are not too high. When the cells are permeabilized relatively slowly but ultimately to a great extent, the kinetics of K+ efflux may be quite complicated.

Effect of ethidium bromide and DEAE-dextran on divalent cation accumulation in yeast. Evidence for an ion-selective extrusion pump for divalent cations

The larger accumulation of Mn2+ than of Sr2+ in Saccharomyces cerevisiae is ascribed to the operation of a specific extrusion pump, presumably a Ca2+ pump, which has a higher affinity for Sr2+ than for Mn2+. The differences in accumulation levels of Mn2+ and Sr2+ attained after prolonged incubation are completely abolished in cells of which the plasmamembrane has been permeabilized with the polybase DEAE-dextran under isotonic conditions. In the permeabilized cells Sr2+ and Mn2+ accumulation levels are attained as for Mn2+ in intact cells. It is suggested that the accumulation of divalent cations into the permeabilized cells mainly represents their accumulation into the vacuoles. Also the cationic dye ethidium abolishes the differences in Mn2+ and Sr2+ accumulation. The dye increases the accumulation of Sr2+ but decreases that of Mn2+ somewhat. It cannot be distinguished yet whether its action is due to an impairment of the efflux pump or to an increase in the permeability of the plasmamembrane facilitating the divalent cations to be accumulated into the vacuoles. Ethidium does not affect the initial rates of divalent cation uptake into the vacuoles, but it effectively reduces the ultimate accumulation of the divalent cations in the DEAE-dextran permeabilized cells, possibly by competing with the divalent cations for intravacuolar binding sites. Similar results are obtained for the accumulation of Ca2+. It is concluded that the efflux pump enables the yeast cell to regulate accumulation levels of the various divalent cations to different extents.

Characteristics of ethidium uptake by the trypanosomatid flagellates Crithidia fasciculata and Leptomonas seymouri

The uptake of the phenanthridinium ethidium by the trypanosomatids Crithidia fasciculata and Leptomonas seymouri was studied. The time course of uptake of ethidium was biphasic for both organisms, consisting of an initial rapid phase and a protracted slow phase. The characteristics of these phases were consistent with the hypothesis that the initial phase represented specific external binding, while the second phase represented transport into the cells. In L. seymouri the transport phase was inhibited by inhibitors of energy transduction and putative inhibitors of a transport ATPase. Ethidium transport could not be saturated over a large concentration range of ethidium. Phenanthridiniums and related compounds displayed both inhibitory and stimulatory effects on ethidium transport.