Communication plays an important role in the rapid progress of modern society. We live in an age when information is transmitted through many different pathways and in many different forms to influence our daily decisions. However, although we live in communities, we still treasure our individuality. By analogy, the survival of multicellular organisms depends on each cell type retaining its individuality, even though all cellular activities must be coordinated with other cells. Organisms have evolved multiple strategies to achieve this goal, which include long-range interactions mediated by neural or endocrine mechanisms or short-range interactions that include direct physical or cell–cell contact. While the first strategy involves interactions at a distance, one mode of direct communication involves the cell-to-cell transmission of molecules through channels in a specialized cell surface membrane structure, the gap junction.

Gap junctions contain channels that connect neighboring cells. They differ from other membrane channels since they exist between two cells, they are relatively nonspecific, and the molecular movement through the channels occurs by passive diffusion. The gap junctional channels have an apparent selectivity based principally on molecular size, allowing the movement of molecules smaller than 1000 Da, such as cAMP, but preventing the movement of proteins or nucleic acids. Small informational molecules, such as certain morphogens, could be directly transmitted between cells via gap junctions. Consequently, this type of communication is an important mechanism for regulating events between cells during embryogenesis (