FREEZE‐FRACTURE STUDY OF THE OCCURRENCE OF PLASMA MEMBRANE DIFFERENTIATIONS IN HUMAN BASAL CELL CARCINOMA

ABSTRACT Freeze‐fracture electron microscope technique was used to study the plasma membrane ultrastructure of basal cell carcinoma (BCC) cells biopsied from two patients. Freeze‐fracture replicas of the plasma membrane of BCC cells indicated the presence of gap junctions, tight junctions and desmosomes. Tight junctions were found on almost all fracture faces of BCC cell plasma membranes, while they were seldom found in the normal keratinocytes or basal cells. These tight junctions appeared as an incomplete network of anastomosing strands with many free‐ending spurs. The frequency of gap junctions seemed to increase in number but decrease in size as compared with normal keratinocytes. Many of the gap junctions were associated with tight junctions. Desmosomes varied in size from 0.1 to 1 µm and were found rather frequently. The results of this study indicated that these junctional complexes were very well developed and that these well differentiated junctions may explain the BCC cell's disinclination to metastasize.