1030-8 Changes in β -Actin mRNA Expression in a Canine Model of Left Ventricular Remodeling

Increased expression of the gene coding for the cytoskeletal protein β-actin has been associated with hypertrophy in different cell systems, however its expression in cardiac tissue following myocardial injury remains largely uncharacterized. β-actin mRNA expression was examined in a canine model of left ventricular damage caused by transmyocardial, direct current shock which results in remodeling of the undamaged myocardium. Myocardial RNA was harvested from the LV of normal, unshocked dogs and from the LV distant from the scar 24 hours, 72 hours, 5 days, 10 days and 30 days after DC shock. Northern analysis indicated a 3-fold increase in β-actin mRNA expression that was sustained 5 to 30 days following DC shock. Reverse transcriptase (RT) PCR was also used to examine β-actin mRNA expression with primers derived from the human β-actin sequence. A 297 bp PCR product was generated from amplification of normal canine LV tissue. Amplification of LV tissue from DC-shocked animals resulted in a progressive change from a 297 bp to a 472 bp PCR product. The ratio of 297/472 bp product was 9/1 24 hours after shock. From 3 to 5 days after shock, RT-PCR resulted in approximately equal generation of 297 and 472 bp product. Ten to 30 days after shock the 472 bp product represented over 85% of the β-actin PCR product generated. Sequencing of these PCR products confirmed that both were closely related to β-actin. The observed change in β-actin could represent alternate splicing of a single gene or expression of two different β-actin genes. Differential expression of β-actin mRNA in canine myocardium may contribute-to the already documented growth of the viable myocardium in this model.