Gap junction-mediated cell-to-cell communication in endocrine glands—molecular and functional aspects: a review

It is well established that most signals supporting intercellular communication are produced either at distance or in the local environment of the target cells. From the pioneering work of Kanno and Loewenstein (1), it has become clear that, in most tissues, adjacent cells can communicate in a more direct way, without dilution of the signalling molecules in extracellular compartments. This mode of communication is taking place through specialized structures, named gap junctions, that allow the cellto-cell exchange of cytoplasmic molecules through aqueous channels joining adjacent cells. Gap junctions provide a pathway for the cell-to-cell diffusion of hydrophilic molecules with a molecular mass lower than 1000 D. Cytoplasmic molecules such as ions, metabolites and second messengers are transmitted from cell-to-cell by this way. Such direct exchanges are thought to be of major importance for the overall activity of a given cell population.