Analysis of desmosomal intramembrane particle populations and cytoskeletal elements: detergent extraction and freeze-fracture.

We have examined sections and freeze-fracture replicas of Triton X-100 detergent-extracted desmosomes from murine palatal epithelium. After extraction of lipids as well as soluble proteins, a cytoskeletal framework remained which consisted of intermediate filaments, microfilaments, and intact desmosomal skeletons. Traversing filaments, which link the intermediate filaments to large intramembrane particles of the P-face, appeared undisturbed within the desmosomal skeletons. Compared to unextracted controls, extracted specimens displayed P- and E-face desmosomal intramembrane particles which were more fully exposed. A broad range of sizes and shapes was apparent for the P-face associated particles. E-face particles, some of which were exposed for the first time, were more homogeneous and generally smaller. Statistical data gathered from a large sample of P- and E-face particle diameters disclosed significant differences among the populations of the two faces. Both fracture faces of extracted desmosomal domains displayed a residual surface upon which the exposed particles seemed to remain lodged. The newly revealed structural features are presented in an hypothetical molecular model which provides for both vertical and horizontal stabilization of desmosomal subcomponents. The model may ultimately be relatable to emerging biochemical characterization.