Three-dimensional observation on muscular tissues

Striated muscle cells of frog sartorius and smooth muscle cells of guinea pig taenia coli were observed three-dimensionally by field emission type scanning electron microscope (FE-SEM) and freeze-fracture deep-etching replica (FFDE) method. By tearing at different preparative stages, various cellular structures appeared on SEM: the outer surface of cells, the inner surface of plasmalemma, and the interior of cells. On the inner surface of the plasmalemma of striated muscle, many caveolae, membranous structures and fine filaments were observed. Inside the cells myofibrils showed the characteristic banding pattern and on the thick filaments, a periodicity of 40 nm was observed. Along the myofibril, T-tubules and sarcoplasmic reticulum were seen with their regional differentiations. In smooth muscle cells, on the inner surface of the plasmalemma there were many caveolae, bundles of filaments and endoplasmic reticulum. The central part of smooth muscle cells were occupied by their nucleus, many microtubules, mitochondria and rough surfaced endoplasmic reticulum. By the FFDE method, observations on finer details were added to the SEM studies, including lateral projections of myosin filaments in striated muscles and fine filaments connecting thin myofilaments in smooth muscle cells. In the terminal cistern of the sarcoplasmic reticulum, networks composed of granular materials were observed.