The Journal of Membrane Biology Freeze-Fracture and Morphometric Analysis of Occluding Junctions in Rectal Glands of Elasmobranch Fish

Summary. The structure of occluding junctions in se-cretory and ductal epithelium of salt-secreting rectal glands from two species of elasmobranch fish, the spiny dogfish Squalus acanthias and the stingray Da-syatis sabina, was examined by thin-section and freeze-fracture electron microscopy. In both species, occluding junctions between secretory cells are shal-low in their apical to basal extent and are character-ized by closely juxtaposed parallel strands. Average strand number in the dogfish was 3.5_+0.2 with a mean depth of 56_+5 nm; in the stingray a mean of 2.0 +0.2 strands encompassed an average depth of 18 + 3 nm. In contrast, the linear extent of these junctions was remarkably large due to the inter-meshing of the narrow apices of the secretory cell