A vinculin-containing cortical lattice in skeletal muscle: transverse lattice elements ("costameres") mark sites of attachment between myofibrils and sarcolemma.

Abstract

We have found that vinculin is localized at the sarcolemma of skeletal muscle cells in a two-dimensional orthogonal lattice. Perpendicular to the longitudinal axis of the cell, bands of vinculin encircle the muscle cell and repeat along its length with a periodicity corresponding to the subjacent sarcomeres. Because oftheir appearance and probable function, we call the transverse elements of the lattice "costameres" (Latin costa, rib; Greek meros, part). Costameres have a substructure consisting of densely clustered patches of vinculin; the patches are segregated into two rows which flank the Z line and overlie the I band of the underlying sarcomere. It is likely that the costameres are physically coupled to the underlying myofibrils because: (i) the costameres broaden and narrow in concert with the underlying I band in stretched and contracted muscle, and (ii) adjacent but misaligned myofibrils are mirrored by corresponding discontinuities in the overlying costameres. We hypothesize that the sarcolemmal lattice, detected because vinculin is one of its molecular components, integrates the contractile apparatus with the sarcolemma during lengthening and shortening of the muscle cells.Vinculin (1) has been implicated in cytoskeleton-to-membrane attachment because the smooth muscle protein binds actin (2, 3) and because, in a variety of cell types, vinculin is located at specialized regions where microfilaments abut the plasma membrane. Some examples ofthese specialized regions include the plasma membrane-associated dense plaques ofsmooth muscle cells (4), the fascia adherens ofcardiocytes (5), focal adhesion plaques offibroblasts (1,(6)(7)(8), and the zonulae adherens of the junctional complex in epithelial cells (9).In this paper, we report that vinculin defines a striking, twodimensional lattice associated with the sarcolemma of skeletal muscle cells. Like the hoops and staves of a barrel, this cortical lattice has both longitudinal elements and transverse circumferential elements. We present evidence that the transverse elements of the sarcolemmal lattice ("costameres," from Latin costa, rib, and Greek meros, part) are coupled to the myofibrils.MATERIALS AND METHODS Vinculin was purified to at least 93% homogeneity from frozen (-20°C) glycerinated central muscles of chicken gizzards (10) and used to purify vinculin antibody from rabbit antisera (11). The antibody was tested on immunoblots of total NaDodSO4-soluble muscle proteins separated by NaDodSO4/polyacrylamide gel electrophoresis (12, 13). Thaw-mounted 4-pkm cryostat sections were fixed in phosphate-buffered 3% (wt/vol) paraformaldehyde for 5 min and stained as will be described elsewhere, except that p-phenylenediamine was used to delay fluorescence quenching (14). In control staining protocols, affinity-purified anti-keyhole limpet hemocyanin was used as the first-step antibody. Affinity-purified, fluorescein-coupled, goat anti-rabbit IgG was purchased from Boehringer Mannheim and used as the second-step antibody. Some 4-,um cryostat sections o...

Raver1 is an integral component of muscle contractile elements

“…In striated muscle, the raver1 ligand vinculin is restricted to attachment sites of the contractile apparatus to the sarcolemma, such as costameres and intercalated disks (Tokuyasu et al 1981;Koteliansky and Gneushev 1983;Pardo et al 1983;Witt et al 2004), whereas alpha-actinin, another raver1 binding partner, is additionally present in the Z-disc (Tokuyasu et al 1981;McKenna et al 1986). Thus, we wanted to determine whether raver1 is confined to the costamere or constitutes an integral part of sarcomeric structures.…”

Adaptive strength gains in dystrophic muscle exposed to repeated bouts of eccentric contraction

“…Normally, dystrophin acts in combination with other cytoskeletal proteins in the costameric lattice to connect the sarcomere to the extracellular matrix (11,12). In this capacity, dystrophin helps facilitate the lateral transmission of contractile force and maintains sarcolemmal integrity (5,33,35) and intracellular Ca 2ϩ homeostasis (1,14). The general assumption is that the loss of dystrophin weakens the costameric lattice and renders fibers susceptible to eccentric contraction-induced injury.…”

Biochemical characterization of the soluble form of the junctional plaque protein, plakoglobin, from different cell types

“…It has not been detected, however, in various other kinds of vinculin-containing plaques which are associated with plasma membrane domains bordering on the extra-cellular matrix such as the neuromuscular junctions, the focal densities at the surfaces of muscle and Purkinje fiber cells, and the focal adhesions of cultured cells [36] (for the presence of vinculin in these junstions see [4,5,[38][39][40][41][42][43]). In addition to the plaque-bound form, a significant portion of plakoglobin has been found in supernatant fractions of bovine snout epidermis obtained after homogenization in buffers of near-physiological ionic strength and pH [36].…”