EM 065 Gap Junctions
Gap Junctions
Freeze-fracture electron microscopy of a gap junction. The plasma membranes have been split along their hydrophobic core to reveal the Protoplasmic Face (P-face), tan, and Extracellular Face (E-face; brown).
Each gap junction is composed of protein channels called connexons, made up of six subunits of connexin proteins. When two connexons - one from each neighboring cell - align, they form a continuous channel between the cytoplasm of the two cells.
- Protoplasmic Face (P-face; yellow) - inner layer of the split membrane, adjacent to the cytoplasm
- Gap junctions appear as large clusters of hundreds to thousands of connexons tightly packed in a hexagonal array (not evident in most regions)
- Connexons appear as raised particles
- Extracellular Face (E-face, orange) - outer layer of the opposing membrane, facing the extracellular space.
- Small depressions where connexons are embedded represent the openings of the channels
Courtesy of Judson Sheridan, Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN.