Vinculin is a component of an extensive network of myofibril-sarcolemma attachment regions in cardiac muscle fibers.

Abstract

Immunofluorescent staining of bovine and avian cardiac tissue with affinity-purified antibody to chicken gizzard vinculin reveals 2 new sites of vinculin reactivity. First, vinculin is organized at the sarcolemma in a striking array of rib-like bands, or costameres. The costameres encircle the cardiac muscle cell perpendicular to the long axis of the fiber and overlie the I bands of the immediately subjacent sarcomeres. The 2nd new site of vinculin reactivity is found in bovine cardiocytes at tubular invaginations of the plasma membrane. The frequency and location of these invaginations correspond to the known frequency and distribution of the transverse tubular system in bovine atrial, ventricular and Purkinje fibers. Tubular invaginations that stain with antivinculin were not found in avian cardiocytes and, in fact, a transverse tubular system was not found in avian cardiac fibers. Apparent lateral Z-line attachments to the sarcolemma and its invaginations were observed in cardiac muscle by EM in the same regions where vinculin is found. On the basis of these previous ultrastructural findings and the published evidence for a physical connection between costameres and the underlying myofibrils in skeletal muscle, the immunofluorescence data of this study were interpreted to mean that, in cardiac muscle, vinculin is a component of an extensive system of lateral attachment of myofibrils to the plasma membrane and its invaginations.