INFLUENCE OF TONICITY AND CHLORAMPHENICOL ON HYPERTHERMIC CYTOTOXICITY AND CELL-PERMEABILITY UNDER VARIOUS HEATING RATES

The cell lethality and permeability induced in Escherichia coli B/r, E scherichia coli B-s-l and Zygosaccharomyces bailii cells by high tempe rature (52 degrees C) after heating at different rates (mean s 0.015, 0.25 and 1.50 degrees C per s) and in media of different tonicity and content (isotonic YEP broth versus 0.01 M phosphate buffer, pH7.0 cont aining different concentrations of NaCl) and with versus without chlor amphenicol (10 mu g/ml) have been investigated. Hyperthermic treatment in YEP broth or isotonic 0.01M phosphate buffer resulted in markedly reduced cytotoxicity with decreasing heat rate. The heating rate effec t was larger when the cells were treated in YEP broth. Chloramphenicol , which is known to inhibit expression of heat shock proteins in bacte ria, did not affect the viability of cells or the development of therm otolerance in cells heated at different heating rates in isotonic phos phate buffer but prevented the development of an additional degree of thermotolerance in cells heated slowly in YEP broth. In contrast, the differential effect of heating rate on cytotoxicity and cell permeabil ity was not demonstrated when cells were heated in hypertonic solution (1 M NaCl in 0.01 M phosphate buffer, pH 7.0). It is proposed that he at destabilization of the osmotic cell homeostasis, which is more prof ound after rapid heating, plays a major part in heat induced cellular lethality.