Gap junctions revealed by freeze-fracture electron microscopy

Gap junctions provide the basis for the formation of elaborate networks of communication between cells in animal tissues. Electron microscopic examination of thin sections of plastic embedded gap junctions has provided valuable information on the anatomy and function of these remarkable structures. Freeze-fracture electron microscopy, however, has made available unique vistas of gap junction-bearing intramembrane surface--surface previously inaccessible to the researcher's eyes. Data on population density, distribution, size, geometry of intramembrane particle packing, and structural responses of gap junction components to experimental manipulation are simply and easily obtained with freeze fracture. Recent developments of sophisticated protocols of immunocytochemistry as applied to freeze-fracture replicas further serve to reinforce the notion that freeze-fracture is a powerful tool for study of gap junctions. Molecular techniques of gap junction gene transfection promise to add a truly unique dimension to investigations of the broad spectrum of functional roles of gap junctions.