Gap junction channels

Gap junction channels physically connect adjacent cells, allowing the passage of ions and other small molecules between them and synchronizing cells both electrically and metabolically.  Gap junction channels are composed of two hemichannels (connexons), which are formed from six connexin molecules.  Pannexins are related to connexins and can also form gap junction channels but their expression is limited to the brain, and invertebrate gap junctions are formed by proteins from the innexin family.

Gap junction channels allow the passive diffusion of a variety of molecules including nutrients, metabolites, ions and all known second messengers, allowing electrical and biochemical coupling and enabling synchronized and rapid responses.  Gap junction channels join virtually all cells in solid tissues and play an essential role in a wide range of physiological processes, including cardiac and smooth muscle contraction, regulation of neuronal excitability, epithelial electrolyte transport and keratinocyte differentiation.  

Further reading

Qu and Dahl (2002) Function of the voltage gate of gap junction channels: Selective exclusion of molecules l Proceedings of the National Academy of Sciences. 99(2) 697 PMID: 11805325

Goodenough and Paul (2009) Gap junctions. Cold Spring Harbor perspectives in biology, 1(1) a002576 PMID: 20066080

Dong et al (2018) Gap Junctions in the Nervous System: Probing Functional Connections Using New Imaging Approaches.  Frontiers in Cellular Neuroscience 12 320 PMID: 30283305