Morphologic and biochemical evidence for a contractile cell network within the rat intestinal mucosa

Subepithelial and pericryptal fibroblastlike cells form a two-dimensional network immediately subjacent to the epithelial basal lamina in the small intestine and colon in several mammalian species. Stellate-shaped cells with similar, but not identical characteristics, form a three-dimensional network deep within the villar lamina propria. Electron microscopic studies indicate that these cells contain a putative contractile apparatus, are attached to each other and to apparently organized elements of the extracellular matrix by typical adhesive devices, and form gap junctions with each other. Comparative in situ immunoperoxidase localization studies document the presence in these cells of four contraction-associated proteins (smooth muscle isotropomyosin, cyclic guanosine monophosphate-dependent protein kinase, both nonmuscle and smooth muscle isomyosin, and actin) in amounts generally greater than those found in connective tissue fibroblasts, but less than in smooth muscle cells. Taken together, these results strongly suggest a smooth muscle-like, contractile function for these cells and indicate that this cellular network may provide a supportive tonus for the epithelium, as well as provide the force needed for active movement of the villus, expulsion of crypt secretion products, and propulsion of absorption products in the lamina propria, the microvasculature, and lacteals of the intestinal villus.