Until recently, it was usually assumed that the only source of extracellular ATP acting on purinoceptors was damaged or dying cells, but it is now recognised that ATP release from healthy cells is a physiological mechanism. There is an active debate, however, about the precise transport mechanism(s) involved. There is compelling evidence for exocytotic vesicular release of ATP from nerves, but for ATP release from non-neuronal cells, various transport mechanisms have been proposed, including ATP binding cassette (ABC) transporters, connexin or pannexin hemichannels or possibly plasmalemmal voltage-dependent anion channels (pl-VDAC), as well as vesicular release. During purinergic mechanosensory transduction associated with pain and physiological reflexes, the ATP that acts on P2X₃ and P2X_2/3 receptors on sensory nerve endings is released by mechanical distortion from urothelial cells during distension of bladder and ureter and from mucosal epithelial cells during distension of the colorectum. ATP is released from vascular endothelial cells by shear stress or hypoxia and from odontoblasts, chromaffin cells, immune cells, Merkel cells, epithelial cells in the lung, cancer cells, endocrine cells, keratinocytes in the skin, glomus cells in the carotid body, astrocytes, platelets and red blood cells. Perhaps surprisingly, evidence has been presented that the release of ATP from urothelial cells in the ureter (as well as from endothelial cells) is largely vesicular, since monensin and brefeldin A, which interfere with vesicular formation and trafficking, inhibited distension-evoked ATP release, but not gadolinium, a stretch-activated channel inhibitor, or glibenclamide, an inhibitor of two members of the ABC protein family. A novel mechanism for transport of ATP has been proposed recently that involves activation of the membrane-bound protein cystic fibrosis transmembrane regulator (CFTR) by actin freed from binding by defects of the spectrin cytoskeleton produced by membrane deformation.