ENHANCED GENE-EXPRESSION OF CALCIUM REGULATORY PROTEINS IN STUNNED PORCINE MYOCARDIUM

Objective: Increasing evidence points to a molecular disturbance of Ca 2+ homeostasis in stunned myocardium. The aim of this study was theref ore to investigate the expression of mRNAs for Ca2+ binding proteins r elated 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 o cclusion 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 mR NA rose 2.5-fold at 180 min of reperfusion. A 2.3-fold increase in cal sequestrin mRNAs was observed after 90 min of the second reperfusion. The calmodulin and alpha,beta myosin heavy chain mRNA levels were unch anged. A glyceraldehyde-3-phosphate dehydrogenase cDNA probe served as a reference system. Nuclear run-on assays showed increased transcript ion for Ca-ATPase and calsequestrin at 90 min of reperfusion, supporti ng the view that increased mRNA levels seen with northern hybridisatio n were due to increased transcription of the respective gene. Conclusi ons: The results suggest specific repair mechanisms of stunned myocard ium and point to the involvement of calcium regulatory proteins relate d to the sarcoplasmic reticulum in the pathogenesis of myocardial stun ning.