VALIDITY OF A MODEL OF CULTURED MYOCARDIAL-CELLS FOR ASSESSMENT OF CARDIOPLEGIA

Myocardial protection is usually studied in vitro on perfused heart pr eparations, but never directly on cultured cardiomyocytes. We evaluate d a model of cultured newborn rat cardiomyocytes to study both the cyt otoxicity and the protective effect against chemical hypoxia of three cardioplegic solutions (St Thomas' I, Bretschneider, St Thomas' II) un der normothermic (37 degrees C) and hypothermic (4 degrees C) conditio ns. Cytotoxicity was evaluated in 50% and 100% concentrations of the c ardioplegic solutions with incubation times from 90 to 360 min. Myocar dial protection was studied in 50% cardioplegic solution with metaboli c inhibitors. Immediate and late viabilities, after 24 h of recovery i n the medium, were evaluated by simultaneous staining with fluorescein diacetate and propidium iodide. At 37 degrees C, the 50% concentratio n of the three cardioplegic solutions did not modify cell viability. A t 37 degrees C, with 360 min of incubation, the 100% concentration of the St Thomas' I and Bretschneider solutions diminished immediate viab ility (mean +/- SD: medium 87% +/- 2%, St Thomas' I 58% +/- 5%; Bretsc hneider 37% +/- 8%; St Thomas' II 89% +/- 3%) as well as late viabilit y (medium 69% +/- 2%; St Thomas' I 32% +/- 3%; Bretschneider 24% +/- 7 %; St Thomas' II 65% +/- 4%). At 4 degrees C, immediate and late viabi lities were unaffected by cardioplegic solutions. At 37 degrees C, aft er 360 min incubation time, metabolic inhibitors diminished immediate viability to 29% +/- 1% and late viability to zero. None of the three cardioplegic solutions used at 50% concentration prevented this effect . At 4 degrees C, immediate viability was not significantly affected b y metabolic inhibitors (73% +/- 10%), but the use of Bretschneider car dioplegic solution seemed to be detrimental (53% +/- 9%). On the other hand, recovery phase after pretreatment with metabolic inhibitors wit h or without cardioplegic solutions for 360 min significantly diminish ed late viability (medium 63% +/- 7% metabolic inhibitors 17% +/- 8%; St Thomas' I 17% +/- 6%; Bretschneider 8% +/- 6%; St Thomas' II 15% +/ - 3%) and again cardioplegia was inefficient. In conclusion, in this i n vitro model for the study of cardioplegic solutions, only pure conce ntrations of the St Thomas' I and Bretschneider solutions under normot hermic conditions were cytotoxic. The well-known protective effects of hypothermia against ischemia and reperfusion injury were both reprodu ced. Therefore, and even though cardioplegia failed to have any protec tive effect, probably owing to a severe metabolic inhibition, this mod el may be useful for studying myocardial protection.