Negatively stained punctated cell contacts between luteal cells in rabbit and rat

Cell contacts from rat and rabbit luteal cells have been spread on phosphotungstic acid solution after tissue fractionation or spreading was accomplished by a direct technique avoiding homogenization. Sectioned material was also examined. It was shown by negative staining that the cell contacts were composed of a multitude of bridges. These bridges were either filamentous (condensed form) or clearly showed a larger (expanded form) central particle. The corresponding image in top view showed respectively small and larger granules without any particular arrangement. Large granular structures were also seen on single plasma membranes. Evidence is presented that the condensed and the expanded form are two aspects of the same junctional structure. It is also suggested that both aspects are related to the tightness of the contact. Up to now this type of cell contract has been called "septate-like". However because of the dotted appearance of these contacts after colloidal lanthanum and after negative staining the denomination "punctated cell contact" may be better adapted.