Biochemical and Ultrastructural Studies on Vertebrate Smooth Muscle

Abstract

Three sets of relatively long filaments appear in the cytoplasm of vertebrate smooth muscles. The filaments are distinguished in the electron microscope by their distinctly different diameters, by their subunit fine structure, and by their spatial arrangements. Although there is not good agreement as to the exact diameters of the three sets of filaments, we will refer to them as 8-nm, 10-nm, and 15-nm filaments. Electron microscopic observations have also consistently reported the presence of dense bodies in vertebrate (and invertebrate) smooth muscles. Dense bodies are about 50 nm by 500 nm and are best distinguished at low magnification as clumps of amorphous material. A better name would be amorphous bodies, but for the sake of uniformity we will refer to them as dense bodies.