Distribution and fine structure of the interstitial cells of Cajal.

Distribution and fine structure of the interstitial cells of Cajal were studied in the cat's small intestine. They were only found in the circular muscle layer. They had a slender structure with numerous mitochondria, rough endoplasmic reticulum and granular or secretory vesicles 100 to 300 nm in diameter. The closest distance between the membrane of smooth muscle cells and interstitial cells was 40 to 60 nm. Some nerve bundles were found in close relation to their processes, but neither pre- nor postsynaptic differentiation could be observed. After nialamide treatment the quantity of secretory vesicles increased and therefore it is suggested that these cells have a secretory function producing some kind of peptide and so they may act directly on the smooth muscle cells.