On the structure of isolated junctions between communicating cells

Summary Gap junctions are specialized regions of contact between apposed plasma membranes of communicating cells. They are composed of hexagonally arranged units (connexons) embedded in plasma membranes and linked together in the extracellular space. The three-dimensional structure of the connexon, was obtained by Fourier analysis on specimens of isolated rat liver gap junctions. The connexon is an annular oligomer, composed of six subunits, that protrudes from both sides of the plasma membrane. The subunits are tangentially displaced about the connexon axis. A narrow channel is located along the connexon, axis spanning the thickness of the junction, but it is greatly reduced in the hydrophobic zones of the membranes. Two closely related forms of isolated gap junctions which have different connexon subunit structures but the same hexagonal lattice, were obtained. The transition between the two forms of communicating junctions seen in isolation is produced by radial inward motion of the connexon subunits near their cytoplasmic surfaces and a reduction of their inclination tangential to the 6-fold axis. Similar rearrangement of essentially rigid subunits embedded in the membrane could provide a mechanism for modulation of the junction permeability. Presented in the symposium on Molecular and Morphological Aspects of Cell-Cell Communication at the 31st Annual Meeting of the Tissue Culture Association, St. Louis, Missouri, June 1–5, 1980. This symposium was supported in part by Contract 263-MD-025754 from the National Cancer Institute and the Fogarty International Center. This work was supported by NH Grants 5P1GM23911-07 and 5T32-6M07403-04.