CHANGES IN GENE-EXPRESSION FOLLOWING SHORT CORONARY OCCLUSIONS STUDIED IN PORCINE HEARTS WITH RUN-ON ASSAYS

Objective: Brief coronary occlusions cause upregulation of expression in a wide variety of genes. These changes in tissue mRNA concentration could have been produced by transcriptional or post-transcriptional events. The aim of this study was to discriminate between increased transcription and changes in mRNA stability using run-on assays with isolated myocyte nuclei. Methods: Myocyte nuclei isolated from ischaemic/reperfused and normal myocardium were incubated with labelled ribonucleotides. The radioactive RNA was then hybridised with specific cDNA probes and slot blots were autoradiographed. Results: There was increased transcriptional activity for the proto-oncogenes c-myc, c-jun, jun-B, and jun-D. There were marked increases in transcriptional activity for sarcoplasmic Ca2+-ATPase, calmodulin, phospholamban, and calsequestrin. Strong transcriptional activity was found for the ubiquitin and heat shock protein (hsp27, hsp70) genes, and for PAI-1 and GAPDH. The transcription for the beta myosin heavy chain gene was not altered. Conclusions: Changes in the tissue concentration of mRNA species following brief coronary occlusion and repel fusion are most often the result of altered transcriptional activity. Increased c-fos mRNA concentrations observed in earlier studies cannot be explained by transcriptional activity of myocytes during reperfusion. Calmodulin is strongly transcribed but tissue concentration stays constant. The overall pattern of gene expression is indicative of damage at the molecular level, and calcium binding proteins (among perhaps many others) are in need of repair.