Connexins are a family of proteins present in vertebrates that form intercellular channels in the plasma membranes of adjacent cells. These gap junctions facilitate free passage of ions and various small molecules between the cytoplasm of the cells. Connexins are most commonly named according to their molecular weights, though there are competing nomenclatures. mEGFP fused to connexin Cx43 was employed to visualize gap junctions in the pig kidney cell culture shown in the digital video sequence presented in this section.