Figure 1.

Illustration of the formation and degradation of gap junction plaques and annular gap junctions. Connexin proteins synthesized in the endoplasmic reticulum (ER) oligomerize to form connexon complexes. The connexons are transported to the cell surface and inserted into the plasma membrane where they form hemichannels. These hemichannels can dock with hemichannels of an apposing cell and cluster to form a gap junction plaque, characterized by a 2–4 nm gap between the two cell membranes. Gap junction plaques are removed from the cell surface through endoexocytosis, which results in the formation of an annular gap junction. The annular gap junction is then degraded through lysosomal proteolysis [modified from Ref. (130)].