Direct morphological demonstration of the coexistence of vimentin and desmin in the same intermediate filaments of vascular smooth muscle cells.

The stable coexistence of the intermediate filament proteins desmin and vimentin in vascular smooth muscle cells raises questions about the relative amounts of the two proteins in different individual cells, and the distribution of the two proteins in individual intermediate filaments within each cell. These questions have been explored by double immunofluorescence microscopy and double immunoelectron microscopy on semi-thin and ultrathin frozen sections of chicken aorta. The former studies indicate that there is a surprisingly wide variation in the desmin/vimentin ratio in adjacent smooth muscle cells. The latter studies show that both proteins are present in individual intermediate filaments, in clustered arrays rather than uniformly distributed. These findings extend earlier related results, and suggest that the turnover of intermediate filaments may involve the remodelling of existing filaments rather than their de novo polymerization.