The cytoskeleton in skeletal, cardiac and smooth muscle cells

Abstract

The muscle cell cytoskeleton consists of proteins or structures whose primary function is to link, anchor or tether structural components inside the cell. Two important attributes of the cytoskeleton are strength of the various attachments and flexibility to accommodate the changes in cell geometry that occur during contraction. In striated muscle cells, extramyofibrillar and intramyofibrillar domains of the cytoskeleton have been identifi ed , Evidence of the extramyofibrillar cytoskeleton is seen at the cytoplasmic face of the sa rcolemma in striated muscle where vinculin- and dystrophin-rich costameres adjacent to sarcomeric Z lines anchor intermedi a te filaments that span from peripheral myofibrils to the sarcolemma. Intermediate filaments also link Z lines of adjacent myofibrils and may, in some muscles, link successive Z lines within a myofibril at the surface of the myofibril. The intramyofibrillar cytoskeletal domain includes elastic titin filaments from adjacent sarcomeres that are anchored in the Z line and continue through the M line at the center of the sa rcomere; inelastic nebulin filaments also anchored in the Z line and co-extensible with thin filaments; the Z line, which also anchors thin filaments from adjacent sarcomeres; and the M line, which forms bridges between the centers of adjacent thick filaments, In smooth muscle, the cytoskeleton includes adherens junctions at the cytoplasmic face of the sarcolemma, which a nchor B-actin filaments and intermediate filaments of the cytoskeleton, and dense bodies in the cytoplasm, which also anchor actin filaments and intermediate filaments and which may be the interface between cytoskeletal and contractile elements.