Molecular Biology of Gap Junction Proteins

Virtually every animal cell type forms gap junctions, the specialized regions of the cell membrane where adjacent cells concentrate channels for direct cell-to-cell exchanges of cytoplasmic ions and small molecules (1–4). Although the structure, tissue distribution and biophysical characteristics of gap junctions as well as the regulation of the intercellular communications they mediate have been the subject of numerous studies in the last three decades, an indepth analysis of the biochemistry of the proteins comprising gap junctions and of the molecular biology of the encoding genes has been possible only in the last few years (2–4). These recent developments have not completely elucidated all the intriguing questions which are raised by the existence of direct exchanges of cytoplasmic constituents between nearby cells, particularly inasmuch as the physiological function and meaning of these exchanges is concerned. However, they have clearly identified gap junction proteins as the members of amultigene family of highly conserved molecules, which have rather unique characteristics and are essentially ubiquitous in multicellular, mesozoa, and metazoa organisms (2–4).