Electron microscopic contrast of the cytoskeleton and junctional complexesof intestinal epithelial cells by ethanolic phosphotungstic acid

After glutaraldehyde fixation and treatment with ethanolic phosphotungstic acid (E-PTA) before plastic embedding, sections of rat large intestine show ed a characteristic electron contrasting pattern in epithelial cells. The a xis of microvilli, terminal web, a thin band below the luminal plasma membr ane, centrioles and junctional complexes (tight junctions, adherens junctio ns, and desmosomes) appeared highly contrasted. In addition to protein comp onents of microfilaments and intermediate filaments, proteins from the junc tional complexes could also be implicated in the contrasting reaction with E-PTA. Mitochondrial membranes, chromatin masses, and nucleoli of enterocyt es showed considerable electron density, whereas no reaction was found in t he,glycocalyx and mucin content of goblet cells. The clear visualization of cytoskeleton elements and junctional complexes by E-PTA contrasting repres ents a simple and valuable method for studies on the normal and pathologica l organization of these structures in epithelial cells.