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(A) A three-dimensional drawing showing the interacting plasma membranes of two adjacent cells connected by gap junctions. The apposed lipid bilayers (red) are penetrated by protein assemblies called connexons (green), each of which is formed by six connexin subunits. Two connexons join across the intercellular gap to form a continuous aqueous channel connecting the two cells. (B) The organization of connexins into connexons and connexons into intercellular channels. The connexons can be homomeric or heteromeric, and the intercellular channels can be homotypic or heterotypic.