Glucocorticoids improve calcium cycling in cardiac myocytes after cardiopulmonary bypass.
BACKGROUND
Glucocorticoids 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.


METHODS
Piglets (5-7 kg) underwent CPB and 120 min of hypothermic circulatory arrest with (CPB-GC) or without (CPB) methylprednisolone (30 mgkg(-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 120 min 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 120 min after CPB. Calpain activation in myocardium was measured by fluorometric assay.


RESULTS
Preload recruitable stroke work in vivo 120 min 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±168 nM) compared with controls (1127±126 nM, P<0.05) but was maintained in CPB-GC (1021±155 nM, 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).


CONCLUSIONS
The 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.
Pearl
Jeffrey M
JM
Division of Cardiothoracic Surgery, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA.
Plank
David M
DM
McLean
Kelly M
KM
Wagner
Connie J
CJ
Duffy
Jodie Y
JY
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002154:Calpain / Q000378:metabolism; D002315:Cardiopulmonary Bypass / Q000009:adverse effects*; D005938:Glucocorticoids / Q000494:pharmacology* / Q000627:therapeutic use; D006321:Heart / Q000187:drug effects / Q000502:physiology; D008775:Methylprednisolone / Q000494:pharmacology / Q000627:therapeutic use; D023421:Models, Animal; D015428:Myocardial Reperfusion Injury / Q000209:etiology / Q000378:metabolism / Q000517:prevention & control*; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism; D013552:Swine; D000099211:Phospholamban
D002118:Calcium; D002135:Calcium-Binding Proteins; D002154:Calpain; D005938:Glucocorticoids; D008775:Methylprednisolone; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000099211:Phospholamban