Ultra-high resolution scanning electron microscopic studies on the sarcoplasmic reticulum and mitochondria in various muscles: a review.

The three-dimensional structure of the sarcoplasmic reticulum (SR), transverse (T)-axial tubular system and mitochondria in various muscles was examined by means of ultra-high resolution scanning electron microscopy (SEM) after removal of the cytoplasmic matrices and myofilaments by the aldehyde-osmium-DMSO-osmium procedure. The striated muscles reviewed and presented are twitch and slow fibers of the frog, twitch and slow fibers of the chicken, twitch extrafusal fibers and intrafusal fibers of the rat, and cardiac muscle fibers of the rat and dog. In all of these striated muscle fibers, T-tubules run transversely and are coupled with terminal cisternae forming triads or dyads. Sarcotubules arising from the terminal cisterna form meshes around the myofibrils. Considerable variations are seen in the location of the T-tubules, the structure of the terminal cisternae, the SR and the mitochondria among these muscles. The changes of these organelles in the experimental pathological conditions, (i.e., experimental mitochondrial myopathy and hypertrophic myocardium of spontaneously hypertensive rats) are also presented. In addition the SR and mitochondria in the smooth muscles of the rodents are described and discussed.