Biomedical subjects

Eric Ferret

Publications and source records attributed to Eric Ferret.

4 recordsLinked to original sources

PubMed2006

Yeast survival during thermal and osmotic shocks is related to membrane phase change.

The aim of this work was to study the survival of yeast cells exposed to a combination of thermal and osmotic treatments, as occurs during drying processes, and assess associated changes in fluidity of the plasma membrane, which have been studied previously in this laboratory. Cells that were maintained at a nonlethal dehydration temperature (5 or 30 degrees C) were rapidly dehydrated up to 120 MPa, and then thermal stress was suddenly applied between 5 and 30 degrees C. Cell viability was measured after a return to initial conditions (i.e., 1.38 MPa and 25 degrees C). Results showed that the viability of yeast cells exposed to identical combined thermal and osmotic treatments was dependent on the chronology of the stress application. Finally, the temperature at which the dehydration was conducted, up to 120 MPa, appeared to be the main factor involved in cell survival and could be related to fluidity variations of the plasma membrane.

Anisotropy↗

PubMed2006

Yeast cell inactivation related to local heating induced by low-intensity electric fields with long-duration pulses.

The effects of electric field (EF) treatments on Saccharomyces cerevisiae viability were investigated using a PG200 electroporator (Hoefer Scientific Instrument, San Fransisco, CA, USA) with specific attention to induced thermal effects on cell death. Lethal electric fields (1.5 kV cm(-1) for 5 s) were shown to cause heat variations in the cell suspension medium (water+glycerol), while corresponding classical thermal treatments at equivalent temperatures had no effect on the cells viability. Variations of the electrical conductivity of the intra- and extracellular matrix caused by ions and solutes transfer across the membrane were shown to be involved in the observed heating. The results permitted to build a theoretical model for the temperature variations induced by electric fields. Using this model and the electrical conductivity of the different media, a plausible explanation of the cell death induced by low-intensity electric fields with long-duration pulses has been proposed. Indeed, cell mortality could in part be caused by direct and indirect effects of electric fields. Direct effects are related to well known electromechanical phenomena, whereas indirect effects are related to secondary thermal stress caused by plasma membrane thermoporation. This thermoporation was attributed to electrical conductivity variations and the corresponding intracellular heating.

Colony Count, Microbial↗

PubMed2005

Responses of Saccharomyces cerevisiae to thermal stress.

We studied the mechanisms involved in heat gradient-induced thermotolerance of Saccharomyces cerevisiae. Yeasts were slowly heated in a nutrient medium from 25 to 50 degrees C at 0.5 degrees C/min or immediately heat shocked at 50 degrees C, and both sets of cultures were maintained at this temperature for 1 h. Cells that had been slowly heated showed a 50-fold higher survival rate than the rapidly heated cells. Such thermotolerance was found not to be related to protein synthesis. Indeed Hsp104 a known protein involved in yeast thermal resistance induced by a preconditioning mild heat treatment, was not synthesized and cycloheximide addition, a protein synthesis inhibitor, did not affect the thermoprotective effect. Moreover, a rapid cooling from 50 to 25 degrees C applied immediately after the heat slope treatment inhibited the mechanisms involved in thermotolerance. Such observations lead us to conclude that heat gradient-induced thermal resistance is not directly linked to mechanisms involving intracellular molecules synthesis or activity such as proteins (Hsps, enzymes) or osmolytes (trehalose). Other factors such as plasma membrane phospholipid denaturation could be involved in this phenomenon.

Adaptation, Physiological↗

PubMed2003

Cell volume changes during rapid temperature shifts.

The effect of a rapid temperature increase on the volume of different types of cells was investigated. Experiments were carried out using continuous microscopic image analysis. Volume variation of yeast cells, yeast spheroplasts and human leukaemia cells was measured during the transient phase after a thermal shift. The thermal shift was found to induce rapid increase in cell volume for cells lacking a cell wall (yeast spheroplasts and human leukaemia cells). This increase in cell volume is assumed to be a main cause of the heat shock-induced cell death. A theoretical mechanistic model that explains the behaviour of these cells is finally proposed.

Cell Size↗