The interstitial cells of Cajal of the rat stomach. A light and electron microscope study

Interstitial cells of Cajal (ICC), presumed to have a smooth muscle-like nature and to play a pacemaker role, are usually identified for their peculiar ultrastructural features and specific location throughout the gut muscle wall. A Zinc-Iodide-Osmium (ZIO) impregnation for ICC identification under the light microscope has been proposed. However, controversies as to certain ICC identification under both light and electron microscopes are still present, due to their ultrastructural features somewhat similar to the fibroblast ones and the low specificity of the ZIO-staining. The rat stomach has been studied. Some specimens have been routinely processed for electron microscopy, some others have been ZIO-impregnated and further routinely processed for both light and electron microscopy, in order to assure that all the cells presumed to be ICC for their ZIO-staining affinity are the same cells identified as ICC with routine electron microscope procedures, and not fibroblasts. The routine electron microscope examination made it possible to identify within the rat gastric muscle coat two cell populations, one with the same location and morphology as those reported in literature for the gastric ICC, and a second one with a similar location, but showing undoubted fibroblastic features. ZIO-staining, under both light and electron microscopes, revealed ZIO-stained cells distributed within the muscle coat in a manner identical to that of the ultrastructurally identified ICC. Under electron microscope examination, this cell type only was fully impregnated by the zinciodide deposits, whereas all other cell types, including fibroblast-like cells, were devoid of them. These data confirm that ICC can be electively ZIO-stained and that these cells and fibroblasts are two distinct cell types, as ultrastructural and physiological reports had previously suggested.