Background: Chronic, disease-associated oxidative stress induces myocardial peroxynitrite formation that may lead to nitrosative inhibition of the calcium cycling protein sarcoplasmic endoreticular calcium adenosine triphosphatase subtype 2a (SERCA2a). The current study was designed to test the hypothesis that the acute oxidative stress associated with lung resection also induces myocardial nitrosative stress and alters SERCA2a activity.
Methods: Ventricular myocardium from 16 swine was studied; 11 animals had undergone left upper lobectomy (n = 7) or sham thoracotomy (n = 4) 3 days before harvest, and 5 were nonoperated controls. Tissue peroxynitrite was assessed by measurement of 3-nitrotyrosine incorporation into proteins. SERCA2a activity was determined from indo-1 uptake by isolated sarcoplasmic reticular membranes. Expression of SERCA2a and its regulatory protein phospholamban were determined by Western blotting, as was the phospholamban phosphorylation state (when dephosporylated, phospholamban inhibits SERCA2a). Mechanical significance of changes in SERCA2a activity was assessed from the force-frequency relation of isometric myocardial trabeculae.
Results: Relative to both the control and sham groups, lobectomy animals exhibited a greater than twofold higher myocardial 3-nitrotyrosine incorporation and an approximately 50% lower SERCA2a activity, but no difference in SERCA2a or phospholamban expression or phospholamban phosphorylation. Concomitantly, whereas the trabecular force-frequency relation of control animals was positive, that of lobectomy animals was negative, consistent with impaired calcium cycling.
Conclusions: These data indicate that oxidative/nitrosative stress associated with lung resection influences SERCA2a activity independent of any influence on protein expression or phospholamban phosphorylation. The findings link an acute event with a subcellular process primarily described for chronic illness and suggest a biochemical basis for perioperative changes in myocardial mechanical reserve.