Gap junctions belong to the type of communicating junctions. Their function is to provide direct communication between the cytoplasm of neighboring cells. Each of these neighboring membranes forms a hemichannel called connexon. The connexons constitute aggregates (clusters), which are defined as groups of closely packed intramembrane particles on the Р face of a fractured membrane. The intramembrane particles on the P face correspond to their matching pits on the E face.

An exactly identical cluster of hemichannels is also formed on the membrane of a neighboring cell; membranes approaching, the hemichannels are positioned accurately beside each other thanks to adhesive properties of their proteins. Thus, a group of enclosed channels is organized connecting the cytoplasm of the cells. The lumen of these channels is large enough for a passage of ions and small molecules with a diameter of about 1.5 nm. Among them, one may also find minor signaling molecules such as cyclic adenosine monophosphate (cAMP). They help to provide metabolic and signaling cell cooperation, which arranges the collective activity. The channels of gap junctions are Ca²⁺-dependent; it means that a local increase of Ca²⁺ concentration directly near the connexons leads to a blocking of channels and cell disconnection.