Roles of compatible osmolytes and heat shock protein 70 in the induction of tolerance to stresses in porcine endothelial cells

Studies of the responses of porcine pulmonary endothelial cells to acute hypertonic stress have been extended by examining the induction and underlying mechanisms of cell tolerance to both osmotic and heat stresses. Preliminary adaptation of these cells to 0.4 osmol (kg H2O)(-1) rendered them tolerant either to subsequent severe osmotic stress (0.7 osmol (kg H2O)(-1)) or to subsequent severe heat shock (50 min at 49degreesC). In contrast, preliminary exposure of the cells to mild heat shock (44degreesC for 30 min) induced tolerance only to severe heat shock, not to hyperosmotic stress. Induction of tolerance to heat shock by either procedure correlated with the induced expression of heat shock protein 70 (HSP70). Induction of tolerance to hyperosmotic stress, on the other hand, was associated with the cellular accumulation of osmolytes, such as amino acids, betaine and myo-inositol, and did not correlate with the induced expression of HSP70. It also required a reduction in the final change of osmotic pressure applied to the cells, such that maximum cell shrinkage would not be much more than 40%. In general, therefore, HSP70 and compatible osmolytes have distinct roles in cellular adaptation to these stresses.