A study of post-secretory maturation ameloblasts in the cat by transmission and freeze-fracture electron-microscopy.

Permanent canine and molar tooth germs of kittens were processed for thin-sectioning and freeze-fracture replication. Maturation ameloblasts were divided into ruffle-ended (RA), smooth-ended (SA) and intermediate (IA). RA had an extensive distal ruffled border consisting of deep membrane invaginations, forming complicated extracellular channels. Adjacent RA were connected by extensive distal junctional complexes (zonulae occludentes). The SA had flattened distal cell surfaces and few coated and smooth vesicles in the distal cytoplasm. Adjacent SA were connected by proximal zonulae occludentes, but had only maculae occludentes at their distal ends so permitting broad lateral extracellular spaces to communicate directly with the enamel surface. IA near the RA layer had a ruffled border consisting of deep and narrow membrane invaginations and pinosomes filled with granular material. IA next to the SA layer had no ruffled border but had pinosomes that seemed to originate directly from the distal cell surfaces. IA were polarized and connected by proximal and distal junctional complexes consisting of either zonulae or fasciae occludentes and associated gap junctions.