RESUMO
Even though endothelin is recognized as an important vasoregulatory molecule, the roles of endothelin receptors in specific cell types are not yet fully understood. Mice with a null mutation in endothelin A receptor gene (ET(A)) or in the gene of its ligand (endothelin 1) die neonatally due to craniofacial and cardiac abnormalities. This early lethality has in the past hindered studies on the role of endothelin in cardiovascular physiology and pathophysiology. To overcome this obstacle, we utilized the cre/loxP technology to generate mice in which the ET(A) gene could be deleted specifically in cardiomyocytes. The cre recombinase transgene driven by the alpha-myosin heavy-chain promoter deleted the floxed ET(A) allele specifically in the hearts of these mice, resulting in a 78% reduction in cardiac ET(A) mRNA level compared to wild-type controls. Cardiomyocyte-specific ET(A) knockout animals are viable and exhibit normal growth, cardiac anatomy, and cardiac contractility, as assessed by echocardiography. In addition, these animals exhibit hypertrophic and contractile responses to 10-day infusion of angiotensin II or isoproterenol similar to those observed in control animals. These results indicate that in adult mice cardiac ET(A) receptors are not necessary for either baseline cardiac function or stress-induced response to angiotensin II or isoproterenol.