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 e vents. The aim of this study was to discriminate between increased tra nscription and changes in mRNA stability using run-on assays with isol ated myocyte nuclei. Methods: Myocyte nuclei isolated from ischaemic/r eperfused and normal myocardium were incubated with labelled ribonucle otides. The radioactive RNA was then hybridised with specific cDNA pro bes 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 fo r sarcoplasmic Ca2+-ATPase, calmodulin, phospholamban, and calsequestr in. Strong transcriptional activity was found for the ubiquitin and he at shock protein (hsp27, hsp70) genes, and for PAI-1 and GAPDH. The tr anscription for the beta myosin heavy chain gene was not altered. Conc lusions: Changes in the tissue concentration of mRNA species following brief coronary occlusion and repel fusion are most often the result o f altered transcriptional activity. Increased c-fos mRNA concentration s observed in earlier studies cannot be explained by transcriptional a ctivity of myocytes during reperfusion. Calmodulin is strongly transcr ibed but tissue concentration stays constant. The overall pattern of g ene expression is indicative of damage at the molecular level, and cal cium binding proteins (among perhaps many others) are in need of repai r.