Yeast membrane fluidity, potassium fluxes and extra cellular pH in relation to glucose availability

Abstract

Glucose has many effects on the yeast Saccharomyces cerevisiae mediated via complex signal transduction processes. We found that membranes of yeast cells in the presence and absence of glucose are characterized by high and low membrane fluidities, respectively. This study examines the effects of glucose availability on membrane fluidity, K+ fluxes and pH. Fluidity was assessed by measuring fluorescence anisotropy in vivo in cells labelled with diphenyl hexatriene. Addition of glucose to starved and washed yeast cultures caused a rapid decrease in membrane fluidity, acidification of the medium and uptake of K+. Where K+ was not limiting, a second phase of increasing membrane fluidity resulted in high membrane fluidity characteristic of cells growing on glucose. Na+ did not substitute for K+ in cation uptake or initiation of fluidity increase, and the K+ channel blocker Ba2+ slowed both acidification and K+initialed fluidity increase. In conclusion, the nature of the membrane fluidity changes in response to glucose has been partly elucidated. This long-term fluidity change appears to require both a basal level of cytoplasmic K+ and re-eslablishment of normal fermentative metabolism.