Analysis of intracellular pH in the yeast Saccharomyces cerevisiae under elevated hydrostatic pressure: a study in baro- (piezo-) physiology.
Hydrostatic pressure is a distinctive feature of deep-sea environments, and this thermodynamic parameter has potentially inhibitory effects on organisms adapted to living at atmospheric pressure. In the yeast Saccharomyces cerevisiae, hydrostatic pressure causes a delay in or cessation of growth. The vacuole is a large acidic organelle involved in degradation of cellular proteins or storage of ions and various metabolites. Vacuolar pH, as determined using the pH-sensitive fluorescent dye 6-carboxyfluorescein, was analyzed in a hydrostatic chamber with transparent windows under elevated hydrostatic pressure conditions. A pressure of 40-60 MPa transiently reduced the vacuolar pH by approximately 0.33. A vma3 mutant defective in vacuolar acidification showed no reduction of vacuolar pH after application of hydrostatic pressure, indicating that the transient acidification is mediated through the function of vacuolar H(+)-ATPase. The vacuolar acidification was observed only in the presence of fermentable sugars, and never observed in the presence of ethanol, glycerol, or 3-o-methyl-glucose as the carbon source. Analysis of a glycolysis-defective mutant suggested that glycolysis or CO2 production is involved in the pressure-induced acidification. Hydration and ionization of CO2 is facilitated by elevated hydrostatic pressure because a negative volume change (delta V < 0) accompanies the chemical reaction. Moreover the glucose-induced cytoplasmic alkalization is inhibited by elevated hydrostatic pressure, probably because of inhibition of the plasma membrane H(+)-ATPase. Therefore, the cytoplasm tends to become acidic under elevated hydrostatic pressure conditions, and this could be crucial for cell survival. To maintain a favorable cytoplasmic pH, the yeast vacuoles may serve as proton sequestrants under hydrostatic pressure. We are investigating the physiological effects of hydrostatic pressure in the course of research in a new experimental field, baro-(piezo-) physiology.
Japan Marine Science and Technology Center, Yokosuka, Japan. abef@jamstec.go.jp
F
F
Abe
K
K
Horikoshi
D004777:Environment; D005452:Fluoresceins; D005456:Fluorescent Dyes; D005656:Fungal Proteins / Q000235:genetics; D005800:Genes, Fungal; D006863:Hydrogen-Ion Concentration; D006874:Hydrostatic Pressure; D007424:Intracellular Fluid / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation; D006180:Proton-Translocating ATPases / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D014617:Vacuoles / Q000378:metabolism
D005452:Fluoresceins; D005456:Fluorescent Dyes; D005656:Fungal Proteins; C087287:VMA-3 protein, Neurospora crassa; C024098:6-carboxyfluorescein; D006180:Proton-Translocating ATPases