Dystrophin (Xp21), a new phenotype marker of cultured rat aortic myocytes

Dystrophin is a low-abundance cytoskeletal protein involved in the maintenance of membrane integrity in striated muscle. Very little is known about its role in smooth muscle. Utrophin (a dystrophin-related protein) is an ubiquitous protein whose role is still unclear. Changes in the expression of both proteins (if any) during phenotypic modulation of smooth muscle have not yet been reported. In contrast, modulated expression of heavy-molecular-weight caldesmon (h-CaD), a well-known specific regulatory protein of the contractile apparatus in smooth muscle, is well documented, along with its nonmuscle isoform, low-molecular-weight caldesmon (1-CaD), and other cytoskeletal proteins. We investigated three properties of cultured rat aortic smooth muscle cells: morphology, contractile ability, and expression of dystrophin, utrophin, h-CaD, and 1-CaD. Cells were grown either in serum substitute supplemented medium (U-medium), where they reexpressed contractility, or in fetal calf serum-supplemented medium (F-medium), where they did not. It was found that only cultures grown in U-medium continued expressing dystrophin, even during the proliferation phase, contrary to cells grown in F-medium. However, when F-medium was changed for U-medium the cells recovered their contractility and reexpressed dystrophin. Expression of utrophin, h-CaD, and 1-CaD was similar in both culture types. Dystrophin was demonstrated to be a true phenotype marker of cultured rat aortic smooth muscle cells, particularly with respect to their actual contractility.