Endoexocytosis

Endoexocytosis is a cellular process. It is a unique internalization process in which the two opposing gap junction plaque membranes are internalized into one of two contacting cells, to form pentilaminar-annular gap junction vesicles. In non-gap junctional membrane internalization, endocytosis can occur independent of the conditions in adjacent cells. However in the case of gap junction plaque internalization the membrane of the adjacent cell is internalized into its contacting cell pair, and is thus an “endoexocytic” process. It has been previously suggested that gap junction plaque internalization is mediated by clathrin and its associated proteins. This hypothesis was supported initially, by the presence of the bristle-like coat surrounding annular gap junction vesicles and later by the demonstration of the light microscopic immunocytochemical and transmission electron microscopic quantum dot colocalization of clathrin and Cx43-GFP structures. The reports of a decreased number of annular gap junctions following treatments that disrupt clathrin activity provided additional support for a role of clathrin in gap junction plaque internalization and annular gap junction formation.