nystatin-a1 and tetraphenylphosphonium

The characteristics of the uptake of lipophilic cations tetraphenylphosphonium (TPP+) into Candida albicans have been investigated to establish whether TPP+ can be used as a membrane potential probe for this yeast. A membrane potential (delta psi, negative inside) across the plasma membrane of C. albicans was indicated by the intracellular accumulation of TPP+. The steady-state distribution of TPP+ was reached within 60 min and varied according to the expected changes of delta psi. Agents known to depolarize membrane potential caused a rapid and complete efflux of accumulated TPP+. The initial influx of TPP+ was linear over a wide range of TPP+ concentrations (2.5-600 microM), indicating a non mediated uptake. Thus, TPP+ is a suitable delta psi probe for this yeast.

Topics: Biological Transport; Candida albicans; Cell Membrane; Cell Membrane Permeability; Membrane Potentials; Nystatin; Onium Compounds; Organophosphorus Compounds

In the yeast Rhodotorula glutinis, accumulation of the tetraphenylphosphonium ion (TPP+) was increased under conditions of osmotic stress, indicating a hyperpolarization of the negative membrane potential (delta psi). The following observations were consistent with the occurrence of hyperpolarized delta psi: enhanced accumulation of glucosamine, the uptake of which is also driven by delta psi; increased respiratory rate. The accumulation of TPP+ was gradually decreased by lowering the pH of cell suspensions. At pH values below 4.5, no TPP+ was taken up, but instead thiocyanate (SCN-) was accumulated, indicating a positive delta psi. The pH-dependent influx of glucosamine followed the pattern of TPP+ accumulation both in the wild-type and in the nystatin-resistant mutant, M67, which displayed a negative delta psi down to pH 3. Thus TPP+ accumulation in Rh. glutinis reflected actual electrical potential difference across the plasma membrane.

Topics: Glucosamine; Hydrogen-Ion Concentration; Indicators and Reagents; Membrane Potentials; Mitosporic Fungi; Nystatin; Onium Compounds; Organophosphorus Compounds; Osmotic Pressure; Oxygen Consumption; Pentoses; Rhodotorula

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.

Topics: Carbonyl Cyanide m-Chlorophenyl Hydrazone; Cell Membrane Permeability; Mathematics; Membrane Potentials; Nystatin; Onium Compounds; Organophosphorus Compounds; Potassium; Saccharomyces cerevisiae