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 (By similarity). Homohexamer (By similarity). Forms homomeric or PANX1/PANX2-heteromeric intercellular channels on coexpression in paired Xenopus oocytes. Expressed in the eye, thyroid, prostate, kidney and liver. Abundantly expressed in the CNS, including hippocampus, olfactory bulb, cortex, cerebellum and white matter. S-nitrosylation inhibits channel currents and ATP release. Belongs to the pannexin family.