α-Skeletal actin is associated with increased contractility in the mouse heart

BALB/c mice express abnormally high levels of α-skeletal actin in the heart, which may be related to a duplication in the promoter of the α- cardiac actin gene. To evaluate the effects of overexpression of the α- skeletal actin isoform on cardiac contractile function, we studied these mice using the isolated perfused work-performing murine heart model and measured actin isoform expression in the same hearts. We quantified myocardial contractility from the maximum rate of contraction (+dP/dt) and time to peak pressure and relaxation from -dP/dt and time to half relaxation of left intraventricular pressure. Dot blots of total RNA hybridized against oligonucleotide sequences specific for either α-skeletal or α-cardiac actin mRNA showed that increased levels of α-skeletal actin RNA correlated significantly with increased contractility of hearts from the BALB/c mice (r=.80, n=15, P<.001). The present study demonstrates a significant functional correlation between α-actin isoform content and cardiac contractile function and also that α-skeletal actin may promote an increased contractile function in the heart compared with α-cardiac actin.