Structural component of the gap junctions and the hemichannels. May play a role as a Ca(2+)-leak channel to regulate ER Ca(2+) homeostasis. Homohexamer. Forms homomeric or PANX1/PANX2-heteromeric intercellular channels on coexpression in paired Xenopus oocytes. S-nitrosylation inhibits channel currents and ATP release. Belongs to the pannexin family.