Cell death induced by mild physical perturbations could be related to transient plasma membrane modifications

An understanding of membrane destabilization induced by osmotic treatments is important to better control cell survival during biotechnological processes. The effects on the membranes of the yeast Saccharomyces cerevisiae of perturbations similar in intensity (same amount of energy) but differing in the source type (heat, compression and osmotic gradient) were investigated. The anisotropy of the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene was measured before and after each treatment to assess the reversibility of the membrane changes related to each treatment. Except for heat shock at 75 degrees C, changes in membrane fluidity were reversible after the return to initial conditions, showing that two kinds of physical stress can be distinguished regarding the reversibility of membrane changes: high and mild energy stresses. With the application of osmotic gradients, anisotropy was assessed during treatment with five osmotic pressure levels from 30.7 to 95.4 MPa with two different yeast strains and related to the rate of cell death caused by each stress. The exposure of cells to increasing osmotic pressures involved a progressive lowering of membrane anisotropy during lethal perturbations. Osmotic stresses associated with reversible fluidity changes of increasing intensity in the membrane led to proportional death rates and time-dependent cell death of increasing rapidity during the application of the stress. Finally, a hypothesis relating the extent of membrane structural changes to the kinetic of cell death is proposed.