Costameres were identified, for the first time, in skeletal and cardiac muscle, as regions associated with the sarcolemma, consisting of densely clustered patches of vinculin; they have many characteristics common to the cell-extracellular matrix-type of adherens junctions. Costameres are considered ‘proteic machinery’ and they appear to comprise two protein complexes, the dystrophin-glycoprotein complex (DGC) and the vinculin-talin-integrin system. In comparison to skeletal muscle, few studies have focused on cardiac muscle regarding these two complexes, and study is generally relative to dystrophin or to cardiac diseases, such as cardiomyopathies. However, insufficient data are available on these proteins in healthy human cardiomyocytes. For this reason, we performed an immunohistochemical study using human cardiac muscle fibers, in order to define the real distribution and the spatial relationship between the proteins in these two complexes. Our data showed a real costameric distribution of DGC and of the vinculin-talin-integrin system; all tested proteins were present in T-tubule and in intercalated disks. Moreover, our data demonstrated that all tested proteins of DGC colocalized with each other, as all tested components of the vinculin-talin-integrin system, and that all tested proteins of DGC colocalized with all tested proteins of the vinculin-talin-integrin system. Finally, all tested proteins of the two complexes were localized in the region of the sarcolemma over the I band, in 100% of our observations. The present study, for the first time, analyzed the majority of proteins of DGC and of the vinculin-talin-integrin system in cardiac muscle fibers, and it confirmed that DGC and the vinculin-talin-integrin system have a role in the transduction of mechanical force to the extracellular matrix. Finally it attributed a key role in the regulation of action potential duration to cardiac myocytes.

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