An open gap junction, composed of six identical connexin proteins. Each of these six units is a single polypeptide which passes the membrane four times (referred to as four-pass transmembrane proteins).
Connexins, or gap junction proteins, are a family of structurally related transmembrane proteins that assemble to form vertebrate gap junctions (an entirely different family of proteins, the innexins, form gap junctions in invertebrates). Each gap junction is composed of two hemichannels, or connexons, which are themselves each constructed out of six connexin molecules. Gap junctions are essential for many physiological processes, such as the coordinated depolarization of cardiac muscle, proper embryonic development, and the conducted response in microvasculature. For this reason, mutations in connexin-encoding genes can lead to functional and developmental abnormalities.