Connexin proteins oligomerize to form intercellular channels, called gap junctions, through which ions and small molecules move between adjacent cells. Connexin 40(Gap junction alpha-5 protein) is a protein that in humans is encoded by the GJA5 gene.This gene is a member of the connexin gene family. The encoded protein is a component of gap junctions, which are composed of arrays of intercellular channels that provide a route for the diffusion of low molecular weight materials from cell to cell. Mutations in this gene may be associated with atrial fibrillation. Alternatively spliced transcript variants encoding the same isoform have been described.