FUNCTION: One gap junction consists of a cluster of closely packed pairs of transmembrane channels, the connexons, through which materials of low molecular weight diffuse from one cell to a neighboring cell. SUBUNIT: A connexon is composed of a hexamer of connexins. SUBCELLULAR LOCATION: Membrane; multi-pass membrane protein. TISSUE SPECIFICITY: Highly expressed in lung. SIMILARITY: Belongs to the connexin family. Alpha-type (group II) subfamily.