Fig. 4.

Images of perimysial collagen cables. A: low-magnification scanning-electron micrograph of perimysial cables running along the side of stretched mouse muscle fibers. B: higher-magnification scanning-electron micrograph of boxed area in A; this close-up of perimysial cables reveals the collagen fibrillar structure. C: sequential confocal images of a perimysial cable being stretched and rotating during imaging. Specimen was labeled with an anti-type I collagen antibody. Sarcomere length is shown in microns; perimysial cable angle is shown in degrees. D: 3-dimensional reconstruction of serial block-face images taken from mouse skeletal muscle color coded for capillaries (pink), fibroblasts (blue), or perimysial collagen cables (yellow). Scale bar = 5 µm. E: high-magnification (×11,000) transmission electron micrograph with stereology grid overlaid. Each point (at crosshair) was classified as a single collagen fibril (green circle), collagen fibril in cable (pink circle), or interstitial space (black). Points lying on objects that were not part of the extracellular space were not classified (red) or included in quantification. Scale bar = 250 nm. F: volume fraction of collagen fibrils located within perimysial cables determined by stereological analysis of transmission electron micrographs from transgenic mice lacking the desmin gene, resulting in fibrosis. (Images taken from studies published in Refs. 21–23.)