Figure 2:

Structure and function of perimysial cables. (A) Confocal microscopic view of a small group of stretched muscle fibers labelled with a type 1 collagen antibody. Note several collagen cables running alongside the fibers. White bars are the same as those in (B). (B) Phase contrast micrograph of fibers shown in A. Note the clearly delineated sarcomeres, but absence of perimysial cables that do not appear with this type of microscopy. White bars show groups of 10-sarcomeres used to calculate sarcomere length which, in this specimen averages ~4.3 µm. Collagen cable angles in (A) and sarcomere lengths in (B) are used for data plotted in (C). (C) Relationship between perimysial cable angle with respect to the long axis of the fiber and average sarcomere length. Note that cables become nearly parallel to fibers as sarcomere length increases. Data represent mean±SEM of 6 cables from two different muscles. (Experiments previously published in Gillies et al., 2017). (D) Sample scanning electron micrograph of one serial blockface section of muscle showing intercellular perimysial cable (PC). To define their structure, PCs are traced through serial sections (Fig. 3) to create three-dimensional reconstructions (Fig. 4).