Hydrostatic pressure promotes the acidification of vacuoles inSaccharomyces cerevisiae

Application of hydrostatic pressure caused a delay or cessation of cell growth in Saccharomyces cerevisiae. The yeast vacuole is an acidic organelle involved in cellular ion homeostasis and degradation of proteins. Hydrostatic pressure promoted the acidification of the vacuoles in the strain IFO 2347. A pressure of 40 to 60 MPa reduced the vacuolar pH, defined using 6-carboxyfluorescein, from 6.05 to 5.88, while a pressure of 20 MPa did not affect the pH. Similar results were obtained with the strain X2180. Bafilomycin A1, a specific inhibitor of vacuolar H(+)-ATPase (V-H(+)-ATPase), caused a significant alkalization of vacuoles in the strain X2180. The pHs rose to 7.34 and 6.84 at both atmospheric pressure and a pressure of 40 MPa, respectively. Meanwhile, vacuolar accumulation of the weak base quinacrine was increased by a pressure of 40 MPa, suggesting that uptake of the dye was induced by the increased pH gradient across the vacuolar membrane.