Identification of intermediate filaments in mature mammalian skeletal muscle by TEM

Abstract

It is generally assumed that desmin in mature striated muscle cells is in the form of intermediate filaments (IFs) and that its primary locus is at or near the myofibrillar Z-lines. Although IFs have been identified by transmission electron microscopy (TEM) in embryonic and adult smooth and cardiac muscle cells and in differentiating or diseased skeletal muscle cells, IFs have rarely been unambiguously visualized in adult skeletal muscle (especially mammalian) cells by TEM. This is due in part to the small amount of IF protein in normal mature skeletal muscle, and in part to the heavily-packed, myofibril-dominated, intracellular cytoskeleton of these cells. In order to help ascertain the possible mechanism(s) of attachment of IFs to myofibrils, our objectives in this study were to identify, by TEM, IFs in adult mammalian skeletal muscle and to study the structural relationship of IFs and the muscle Z-lines.Samples of porcine semitendinosus muscle were removed from mature animals immediately after death, isometrically restrained and fixed in Karnovsky's fixative for 3 hours at 25°C, and processed by conventional methods followed by embedment in Epon-Araldite resin.