Characteristics of neuronal release of ATP.

Recent studies have described a transmitter-like release of ATP in brain. Once released, extraneuronal ATP is rapidly metabolized to adenosine by ecto-ATPase and nucleotidase. Adenosine, through actions at specific receptors, inhibits neuronal firing in the brain. ATP shares these inhibitory actions, presumably by forming adenosine extraneuronally. Caffeine and theophylline probably exert CNS stimulation by antagonizing adenosine's inhibitory actions in the brain. Extracellular ATP occasionally excites quiescent neurons in the cortex. A possible role for ATP as a sensory neurotransmitter is suggested by its excitatory actions on a subpopulation of dorsal horn cells. ATP release has also been described from sensory nerves in the periphery, motor nerves, nerves of the myenteric plexus, bladder, vas deferens, and from adrenal chromaffin cells and platelets. The possibility that ATP might function as a transmitter, co-transmitter or modulator in the peripheral nervous system is discussed.