Enhanced gene expression of calcium regulatory proteins in stunned porcine myocardium

Objective: Increasing evidence points to a molecular disturbance of Ca²⁺ homeostasis in stunned myocardium. The aim of this study was therefore to investigate the expression of mRNAs for Ca²⁺ binding proteins related to the sarcoplasmic reticulum in a porcine model of myocardial stunning. Methods: In 22 anaesthetised pigs, stunning was achieved by one or two cycles of 10 min left anterior descending coronary artery occlusion and reperfusion. Hearts were excised at various timepoints of the protocol. Total RNA was extracted from stunned (experimental) as well as normally perfused (control) myocardium. Results: Northern blot analysis using radioactive cDNA probes revealed that the Ca²⁺-ATPase mRNA levels increased 1.6-fold compared to the control value at 90 min of the second reperfusion. The steady state level of phospholamban mRNA rose 2.5-fold at 180 min of reperfusion. A 2.3-fold increase in calsequestrin mRNAs was observed after 90 min of the second reperfusion. The calmodulin and α,β myosin heavy chain mRNA levels were unchanged. A glyceraldehyde-3-phosphate dehydrogenase cDNA probe served as a reference system. Nuclear run-on assays showed increased transcription for Ca²⁺-ATPase and calsequestrin at 90 min of reperfusion, supporting the view that increased mRNA levels seen with northern hybridisation were due to increased transcription of the respective gene. Conclusions: The results suggest specific repair mechanisms of stunned myocardium and point to the involvement of calcium regulatory proteins related to the sarcoplasmic reticulum in the pathogenesis of myocardial stunning.