Discrimination between fiber populations in mammalian skeletal muscle by using ultrastructural parameters

Stereological techniques are used to obtain quantitative information from electron micrographs from 300 fibers of skeletal muscle from the adult guinea pig. Ultrastructural parameters measured include Z line width, volume of mitochondria, volume and surface area of tsystem, terminal cisternae, and sarcoplasmic reticulum. Histograms, scattergrams, and statistical discriminant analysis are used to analyze the data. The whole fiber population can be separated with 90% success rate into the red and white vastus muscles and the soleus muscle, which are physiologically fast and slow, respectively. The soleus fibers have a Z line wider than 1100 A and smaller amounts of t-system and terminal cisternae than the vastus fibers. The mitochondrial volume of the vastus fibers shows a continuous distribution over a large range (0.1–15%), with the white vastus fibers at the lower end and the red vastus fibers at the higher end.