Influence of deep hypothermia on the tolerance of the isolated cardiomyocyte to ischemia-reperfusion

The influence of deep hypothermia (4 degreesC) during a substrate-free, hyp oxia-reoxygenation treatment was investigated on cardiomyocytes (CM) prepar ed from newborn rat heart in culture in an in vitro, substrate-free model o f ischemia-reperfusion. The transmembranous potentials were recorded with s tandard microelectrodes. The contractions were monitored photometrically. T he RNA messenger (mRNA) and protein expression for protein (HSP70) were ana lysed by RT-PCR (reverse transcriptase-polymerase chain reaction) and Weste rn blotting, respectively. Simultated ischemia (SI) caused a gradual decrea se and then a cessation of the spontaneous electromechanical activity. Duri ng the reoxygenation, the CM recovered normal function, provided that SI di d not exceed 2.5 h. When SI duration was increased up to 4 h, reoxygenation failed to restore the spontaneous electromechanical activity. Conversely, the exposure of the CM to SI together with deep hypothermia decreased the f unctional alterations observed, and provided a complete electromechanical r ecovery after 2.5 h as well as after 4 h of SI. Deep hypothermia. alone fai led to induce HSP70 mRNA and protein production. On the contrary, HSP70 mRI NA production increased after 2.5 and 4 h of deep hypothermia. followed by 1 h of rewarming, proportionally to the duration of the cooling period. Thi s augmentation in mRNA was associated with a rise in HSP70 protein content. In summary, it appeared that deep hypothermia exerts a strong cytoprotecti ve action during SI only, whereas cooling CM before SI has no beneficial ef fect on subsequent SI. Moreover, these results suggested the persistence of a signaling system and/or transduction in deeply cooled, functionally depr essed cells. Finally, CM in culture appeared to be a model of interest for studying heart graft protection against ischemia-reperfusion and contribute d to clarifying the molecular and cellular mechanisms of deep hypothermia o n myocardium, (C) 2001 Academic Press.