Stereological analysis of transverse tubules and sarcoplasmic reticulum isolated from normal and dystrophic skeletal muscle

Abstract

Vesicles isolated from the transverse tubules and sarcoplasmic reticulum of normal and dystrophic chicken skeletal muscle were analyzed for enzymatic activity and examined following freeze-fracture. A stereological procedure was used to determine particle density distributions on the resulting membrane fracture faces. The particle densities measured in this investigation were compared with those of an earlier study on intact muscle. Isolated sarcoplasmic reticulum vesicles showed a characteristically high P-face (cytoplasmic leaflet) particle density (5108 ± 169 particles/ μm 2) and a low E-face (luminal leaflet) particle density (505 ± 57 particles/ μm 2). Transverse tubule fractions showed a high E-face particle density (2346 ± 179 particles/ μ 2) as well as a substantial P-face particle density (1019 ± 129 particles/ μm 2). The high transverse tubule E-face particle density represents a characteristic morphological feature in the same way that the very high P-face particle density is characteristic of sarcoplasmic reticulum membranes. The major morphological alteration in dystrophic membranes was a shift in the E-face particle density distribution of isolated transverse tubules to a lower average particle density. (The E-face particle density of sarcoplasmic reticulum fractions showed no differences.)