Pannexin-1 (PANX1) is an approximately 45 kDa member of the Pannexin family of four-transmembrane channel proteins with a conserved pattern of cysteines. It is expressed on epithelial cells, neuronal and glial cells, cardiac myocytes, T cells, and erythrocytes. Pannexin-1 forms large pore hexameric channels or heteromeric channels with Pannexin 2 and enables the efflux of ATP and UTP. Its conductance is increased in response to hypoxia, isotonic stress, NMDA R activation, and Caspase-3 and -7 activation during apopotosis. Extracellular release of ATP through Pannexin 1 activates P2X7 receptors which in turn induces the closure of Pannexin-1 channels. Pannexin-1 cooperates with P2X7 for inflammasome activation, Caspase-1 activation, and the release of mature IL-1 beta and also regulates T cell activation at the immunological synapse. Alternate splicing generates an additional isoform that lacks the C-terminal four amino acids in the cytoplasmic tail.