Myoid fibrils in epithelial cells: studies of intestine, biliary and pancreatic pathways, trachea, bronchi, and testis.

Cytoplasmic filaments have been studied extensively by electron microscopy, but the histochemical nature of such fibrils in non-keratinizing epithelia has not been systematically investigated. During studies of early arterial lesions we observed structures with the staining properties of myosins in epithelial cells of various organs. The configurational staining, polarization and fluorescence microscopic properties of these myoid structures were compared with those of myofibrils in smooth muscle and classical myoepithelial cells. The following structures showed the characteristics of myofibrils: the terminal web in columnar epithelial cells of intestine, trachea, bronchi, bile ducts, pancreatic ducts and ductus epididymidis, the pericanalicular layer of bile and pancreatic canaliculi, fibers in the caudal tube of spermatids and the flagella of spermatozoa. Cilia, e.g. of respiratory epithelium, tonofibrils in squamous epithelium and nerve axons did not react. These studies indicate significant histochemical differences between cytoplasmic filaments. Different types of intracellular fibrils can be found in the same cell, e.g. in respiratory epithelium.