ABCC6 and ankylosis: Extracellular ATP release occurs through a variety of mechanisms, including tumor necrosis and apoptosis, vesicular exocytosis, active efflux via ATP-binding cassette subfamily C member 6 (ABCC6) and the ankylosis gene product ANK and diffusion via P2RX7 and Pannexin1 channels (10, 11, 19–24).