Immunohistochemical study of the cytoskeleton of osteoblasts in the rat calvaria. Intermediate filaments and microfilaments as demonstrated by detergent perfusion.

We evaluated the cytoskeleton of osteoblasts in the rat calvaria by transmission electron microscopy after perfusion with a mixture of Triton X-100 and glutaraldehyde and immunoelectron microscopy. In osteoblasts, microfilaments (5-6 nm in diameter) and intermediate filaments (10-12 nm) were arranged in networks or bundles, avoiding cell organelles such as mitochondria and the rough-surfaced endoplasmic reticulum. Some of these intermediate filaments were attached to the nucleus and had a double-helix structure. Immunoelectron microscopy demonstrated that these fibers are actin and vimentin filaments, respectively. Intermediate filaments were abundant around the nucleus while microfilaments were abundant around the cell membrane. Microfilaments formed thick bundles around the cell membrane in formative osteoblasts but did not form bundles in resting osteoblasts.