The ability of heat stress and metabolic preconditioning to protect primary rat cardiac myocytes

Primary rat cardiocytes were subjected to either thermal preconditioning for 30 min at 43°C or 20 min metabolic preconditioning (10 mM deoxyglucose, 20 mM lactate, pH 6.5). Eighteen hours later cells were analysed either for hsp 70i expression or subjected to a subsequent lethal heat stress or simulated ischaemia (10 mM deoxyglucose, 20 mM lactate, 0.75 mM sodium dithionite, 12 mM potassium chloride, pH 6.5) for 2 hours and assessed for survival by trypan blue exclusion.Hsp 70i was induced over 100 fold by thermal preconditioning and 30 fold by metabolic preconditioning (p<0.001, p<0.05), hsp 90 was induced 2.71 fold and 2.24 fold (p<0.001, p<0.001) by thermal and metabolic preconditioning respectively, while hsp 60 was not induced by either treatment. Preconditioned cultures had improved survival against subsequent lethal heat stress or simulated ischaemia: Thermal preconditioning reduced death from 69.22% to 52.46% upon subsequent lethal heat stress and from 49.13% to 36.66% upon subsequent lethal simulated ischaemia. Metabolic preconditioning reduced cell death from 51.29% to 33.8% against subsequent lethal heat stress, and from 69.09% to 55.61% upon subsequent lethal simulated ischaemia. A second marker of cell death, the release of lactate dehydrogenase activity into the culture media, was reduced to 65% and 60% of control values for thermally preconditioned cells subjected to lethal heat or lethal simulated ischaemia respectively. Metabolically preconditioned cells demonstrated lactate dehydrogenase activity of 59% and 51% that of control values, when subjected to lethal heat or lethal simulated ischaemia respectively.Abbreviations hsp heat stress protein - hsp 70i inducible 70 kDa heat stress protein - LDH lactate dehydrogenase - PBS phosphate buffered saline