Purine nucleotides.

The existence of nonadrenergic, noncholinergic nerve components in the autonomic nervous system is now well established. They are strongly represented in the gastrointestinal tract of all vertebrates and have been identified in a variety of other organs, including lung, trachea, bladder, esophagus, eye, seminal vesicles, and possibly parts of the vascular and central nervous systems. Their ultrastructural identification and transmission properties are known and their physiological role is beginning to be understood, at least in the gastrointestinal tract. Evidence that ATP is the transmitter released from nonadrenergic, noncholinergic (purinergic) nerves includes: (a) synthesis and storage of ATP in nerves; (b) release of ATP from the nerves when they are stimulated; (c) exogenously applied ATP mimicking the action of nerve-released transmitter, both producing a specific increase in K+ conductance; (d) the presence of Mg-activated ATPase, 5'nucleotidase, and adenosine deaminase, enzymes, which inactivate ATP; (e) drugs (including 2-substituted imidazolines, 2,2'-pyridylisatogen and dipyridamole), that produce similar blocking or potentiating effects on the response to exogenously applied atp and nerve stimulation.