Fig. 1. Schematic representation of a costamere and the focal adhesion complex (FAC). (A) Two laminin receptors, a dystrophin/glycoprotein complex and an integrin receptor complex are among the sarcolemmal structures (Pardo et al., 1983) that link the contractile apparatus of muscle fibres with the surrounding basal lamina. Components of both receptors, i.e. both dystrophin and the integrin-associated cytoskeletal proteins (talin, vinculin, -actinin), co-localise in subsarcolemmal complexes (Pardo et al., 1983) which connect through -actin and the intermediate-filament proteins desmin and vimentin to the Z-disk of skeletal muscle fibres (adapted from Patel and Lieber, 1997; Rybakova et al., 2000). (B) Integrin-based FACs of cultured mesodermal cells bridge cortical -actin to the extracellular matrix (ECM). The inset indicates schematically the proposed involvement of FAK (in red) in the formation of FACs. Occupancy of integrins with ECM ligand (1) causes phosphorylation (orange circle) of integrin-associated FAK (2) which, in turn, promotes recruitment of both cytoskeletal (paxillin, vinculin, talin, -actinin and -actin; coloured in dark green) and signalling molecules (3) (e.g. MAPK and c-src kinase, coloured in light green) to integrins (Miyamoto et al., 1995).