Evolution of gap junction proteins--the pannexin alternative.

Gap junctions provide one of the most common forms of intercellular communication. They are composed of membrane proteins that form a channel that is permeable to ions and small molecules, connecting the cytoplasm of adjacent cells. Gap junctions serve similar functions in all multicellular animals (Metazoa). Two unrelated protein families are involved in this function; connexins, which are found only in chordates, and pannexins, which are ubiquitous and present in both chordate and invertebrate genomes. The involvement of mammalian pannexins to gap junction formation was recently confirmed. Now it is necessary to consider the role of pannexins as an alternative to connexins in vertebrate intercellular communication.