Ultrastrructural Variations of Gap Junctions Correlated with Tissue Types or Funtions.

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1. A simple new method of deep-etching, upside-down etching was developed in an attempt to obtain clearer images of replicas, especially of fresh untreated tissues. During deep-etching, specimens were kept downwards and shaken periodically so that non-volatile materials in the subliming ice could fall out of the frozen tissues. This improvemnet leads to a considerable reduction of sedimented debris of unetchable materials on the membrane surfaces of gap junction plaques.2. Our previous rapid-freeze, deep-etch replica studies have revealed the differences of cytoplasmic surfacesbetween heart and liver gap junction. Further studies were carried out to clarify these differences in various types of tissues.In surface mucous cells of stomach, absorptive epithelial cells of small and large intestine, and distal tubule cells of kidney, similar to the liver gap junctions, most of the cytoplasmic surface membranes were monparticulate. Whereas, in the cardiac atrium and ventricle, aortic endothe … More lium, and the ciliary process, cytoplasmic surface membrane of these non-epithelial gap junctions consistently revealed characteristic particulate patterns like a tiled surface made up of round tiles of vaious sizes. Close examinations disclosed that those granular materials were not merely attached to the membrane surface but protruded from the membrane interior as an integral component of gap junction particles. In the same replica area of pregnant rat uterus at labor, we found that surface membrane of myometrial smooth muscle gap junctions were particulate, but those of endometrial epithelium were smooth.3. The results of present study strongly suggest that cytoplasmic surface structures are different between epithelial and non-epithelial gap junctions; the non-epithelial gap junctions contain the extra cytoplasmic surface domain that is absent in the gap junctions of epithelial origin.It is interesting to note the similar distribution tendency of intermediate filament proteins between epithelial and non-epithelial tissues. Less