Glucocorticoids Improve Calcium Cycling in Cardiac Myocytes After Cardiopulmonary Bypass

BackgroundGlucocorticoids can reduce myocardial dysfunction associated with ischemia and reperfusion injury following cardiopulmonary bypass (CPB) and circulatory arrest. The hypothesis was that maintenance of cardiac function after CPB with methylprednisolone therapy results, in part, from preservation of myocyte calcium cycling.MethodsPiglets (5–7kg) underwent CPB and 120min of hypothermic circulatory arrest with (CPB-GC) or without (CPB) methylprednisolone (30 mg kg−1) administered 6h before and at CPB. Controls (No-CPB) did not undergo CPB or receive glucocorticoids (n = 6 per treatment). Myocardial function was monitored in vivo for 120min after CPB. Calcium cycling was analyzed using rapid line-scan confocal microscopy in isolated, fluo-3-AM-loaded cardiac myocytes. Phospholamban phosphorylation and sarco(endo)plasmic reticulum calcium-ATPase (SERCA2a) protein levels were determined by immunoblotting of myocardium collected 120min after CPB. Calpain activation in myocardium was measured by fluorometric assay.ResultsPreload recruitable stroke work in vivo 120min after reperfusion decreased from baseline in CPB (47.4 ± 12 versus 26.4 ± 8.3 slope of the regression line, P < 0.05), but was not different in CPB-GC (41 ± 8.1 versus 37.6 ± 2.2, P = 0.7). In myocytes isolated from piglets, total calcium transient time remained unaltered in CPB-GC (368 ± 52.5 ms) compared with controls (434.5 ± 35.3 ms; P = 0.07), but was prolonged in CPB myocytes (632 ± 83.4 ms; P < 0.01). Calcium transient amplitude was blunted in myocytes from CPB (757 ± 168nM) compared with controls (1127 ± 126nM, P < 0.05) but was maintained in CPB-GC (1021 ± 155nM, P > 0.05). Activation of calpain after CPB was reduced with glucocorticoids. Phospholamban phosphorylation and SERCA2a protein levels in myocardium were decreased in CPB compared with No-CPB and CPB-GC (P < 0.05).ConclusionsThe glucocorticoid-mediated improvement in myocardial function after CPB might be due, in part, to prevention of calpain activation and maintenance of cardiac myocyte calcium cycling.