Intercellular junctions of the intestinal epithelium in the hagfish (Eptatretus burgeri) were examined by means of the freeze-fracture method. The intestinal epithelium of the hagfish consists of one layer of extremely tall columnar epithelial cells 160μm in height. In thin-section images, occurrence of typical junctional complexes is evident close to the apex of the epithelial cells. In freeze-fracture images, the zonula occludens of the hagfish intestinal epithelium shows a characteristically well-developed configuration. The strands of the zonula occludens number 13.7±2.9 (range 7-9), and the depth measures 1.11±0.34 (range 0.3-2.0)μm. These values indicate that the zonula occludens of the hagfish intestinal epithelium represents an extreme example of the “very tight” type. These well-developed zonula occludens and desmosomes are made to bear intense distortion and stretch caused by the cell movement, because neither the ciliated cell nor the muscular layer is present and the luminal contents are thought to be transported by the movement of the epithelial cells in the hagfish intestine.
Gap junctions on the PF are irregular in shape and consist of densely packed membrane particles 120Å in diameter. The membrane particles of the gap junction do not show typical hexagonal or polygonal arrays which are generally seen in many kinds of cells of other species. Some parts of the gap junction are made of linear arrays of membrane particles. This particulate line sometimes continues to the particulate ridge of the zonula occludens without a distinct border. This finding indicates the possibility that both the zonula occludens and gap junction have common components in the hagfish intestinal epithelium.