ATP released lumenally from umbrella cells is thought to play a role in autocrine signaling while Naloxone benzoylhydrazone release from the serosal surfaces permits interaction with stromal elements including afferent neurons and possibly the detrusor as well. ATP is also released along with norepinephrine by postganglionic parasympathetic nerves that innervate the bladder smooth muscle resulting in a biphasic mechanical response that consists of an initial rapid twitch, followed by a sustained contraction. Upon release, ATP can bind to purinergic receptors of the P2X and P2Y families and initiate ion transport or G-protein-coupled receptor signaling, respectively. P2X receptors, P2X1, P2X2, P2X3, P2X5, P2X6 and P2X7 are differentially expressed throughout the bladder and loss of P2X3 from afferent nerve fibers in a knockout mouse was shown to alter voiding behavior by shifting the micturition reflex to greater fill volumes. P2Y2 and P2Y4 also appear to be expressed indicating a diverse repertoire of purinergic responsive receptors throughout all tissue elements of the bladder. Furthermore, abnormalities in ATP release and in purinergic receptor expression have been noted in numerous studies of human bladder disease as well as in animal models of bladder pathology. These include interstitial RF 9 cystitis, urinary urgency and incontinence, bladder inflammation, spinal cord injury-induced bladder dysfunction, detrusor overactivity and outlet obstruction. While much research has focused on P1 and P2 receptors, purinergic signaling is also critically regulated by ectonucleotidases, which degrade ATP and UTP to their respective nucleosides. These enzymes act to limit, both temporally and quantitatively, the exposure of P2 receptors to their ligands. They also preclude desensitization responses resulting from overstimulation. Furthermore, stepwise conversion creates potent metabolites, like ADP and adenosine, which may then continue to act through other receptors with different affinities and locations. There are four main families of ectonucleotidases; NTPDs, NPPs, alkaline phosphatases and ecto-59-nucleotidase. The families differ primarily in their substrate specificities, with NTPDs highly specific for ATP/UTP/ADP/UDP while NPPs catalyze phosphohydrolysis on a broader range of substrates including lysophospholipids and choline phosphate esters. Alkaline phosphatases are even more promiscuous with broad substrate specificities that overlap with those of the NPPs. Dysregulation of nucleotide metabolism and alterations to the activities of ectonucleotidases has been shown convincingly in many pathological conditions including diabetes, hypertension, acute stroke, chronic renal failure, cancer, myocardial infarction, leukemia and epilepsy.