Cultured Neonatal Rat Cardiomyocytes and 99m Tc-Sestamibi to Assess the Direct Effects of Cardioplegia

The efficacy of cardioplegia in neonatal myocardial protection is still a matter of debate. ^99mTc-sestamibi cellular accumulation reflects sarcolemmal and mitochondrial electrical gradients. It was used to monitor the direct effects of two cardioplegic solutions, modified St Thomas' Hospital and Bretschneider, on normoxic and metabolically-inhibited cultured cells. Cellular accumulation of ^99mTc-sestamibi, expressed by the ratio between intra and extra cellular concentrations, was assessed in three different sets of neonatal rat cardiomyocytes. Cells were either treated with different concentrations of modified St Thomas' solution (50, 75, 100%), they were treated or recovering from a treatment with modified St Thomas and Bretschneider solutions at 50% concentrations, or were recovering from treatment with modified St Thomas' and Bretschneider solution at 50% concentrations mixed with metabolic inhibitors. Cardioplegia depressed the tracer accumulation in a concentration-dependent manner. This effect was independent of the type of cardioplegia (120-min uptake, as a percentage of control values, modified St Thomas' 68 ± 12 and Bretschneider 59 ± 7) and was rapidly reversible. Cardioplegia was unable to prevent the depression of tracer accumulation induced by metabolic inhibitors and even induced a deleterious effect (120-min uptake, as a percentage of control values, metabolic inhibitors 69 ± 12, metabolic inhibitors + modified St Thomas 38 ± 14, metabolic inhibitors + Bretschneider 43 ± 6) during recovery after 30 min of metabolic inhibition. It was concluded that cardioplegia has an apparent detrimental effect on neonatal cardiomyocytes accumulation of ^99mTc-sestamibi during recovery from an ischaemic-like insult.