Ultrastructure of the zinc iodide-osmic acid stained cells in guinea pig small intestine.

This study has demonstrated that cells stained using the zinc iodide-osmic acid (ZIO) method have the same fine structural features as those of fibroblasts. They have a well developed Golgi apparatus, granular endoplasmic reticulum and many mitochondria. They have no basal lamina. They are distributed in association with the deep muscular plexus, within the outer circular muscle layer and in the space between the circular and longitudinal muscle layers. Since this staining method is believed to co-stain nerves and interstitial cells of Cajal, we concluded that these ZIO-positive, fibroblast-like cells represent at least some, if not all, of the interstitial cells which appeared in the original description by Cajal.