This present study describes an experimental approach whereby subcellular 3‐dimensional filamentous structures present within whole cells can be examined, using a conventional transmission electron microscope. This procedure uses cells which have been cultured on carbon‐coated titanium grids, and treated with Triton X‐100 to extract the soluble cytoplasm. Subsequent fixation and critical‐point drying allows filamentous proteins to be easily visualized, due to the increase in contrast produced by removal of the ground cytoplasm. The high resolution obtainable in these preparations permitted an initial classification and description of the filamentous reticulum within cultured presumptive myoblasts. This reticulum is a continuum of filaments and cables, all elements of which appear to be interconnected. These morphological findings were then correlated with the biochemical identification of detergent‐insoluble proteins, of which only actin, myosin, and, perhaps, intermediate filament and LETS protein are the major elements.
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