β-Nicotinamide adenine dinucleotide is an inhibitory neurotransmitter in visceral smooth muscle

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 104; no. 41; pp. 16359 - 16364
• Main Authors: Mutafova-Yambolieva, Violeta N, Hwang, Sung Jin, Hao, Xuemei, Chen, Hui, Zhu, Michael X, Wood, Jackie D, Ward, Sean M, Sanders, Kenton M
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 09.10.2007; National Acad Sciences
• Subjects: Adenosine Diphosphate - analogs & derivatives; Adenosine Diphosphate - pharmacology; Adenosine Triphosphate - pharmacology; Agonists; Animals; Biological Sciences; Cell Line; Electric Stimulation; Energy metabolism; HEK293 cells; Humans; In Vitro Techniques; Mice; Mice, Inbred C57BL; Muscle, Smooth - drug effects; Muscle, Smooth - innervation; Muscles; NAD - physiology; Nerves; Neurons; Neurotransmission; Neurotransmitter Agents - physiology; Neurotransmitters; Purinergic P2 Receptor Antagonists; Purines; Receptors; Receptors, Purinergic P2 - genetics; Receptors, Purinergic P2 - physiology; Receptors, Purinergic P2Y1; Recombinant Proteins - antagonists & inhibitors; Recombinant Proteins - genetics; Recombinant Proteins - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0705510104

Peripheral inhibitory nerves are physiological regulators of the contractile behavior of visceral smooth muscles. One of the transmitters responsible for inhibitory neurotransmission has been reputed to be a purine, possibly ATP. However, the exact identity of this substance has never been verified. Here we show that β-nicotinamide adenine dinucleotide (β-NAD), an inhibitory neurotransmitter candidate, is released by stimulation of enteric nerves in gastrointestinal muscles, and the pharmacological profile of β-NAD mimics the endogenous neurotransmitter better than ATP. Levels of β-NAD in superfusates of muscles after nerve stimulation exceed ATP by at least 30-fold; unlike ATP, the release of β-NAD depends on the frequency of nerve stimulation. β-NAD is released from enteric neurons, and release was blocked by tetrodotoxin or ω-conotoxin GVIA. β-NAD is an agonist for P2Y1 receptors, as demonstrated by receptor-mediated responses in HEK293 cells expressing P2Y1 receptors. Exogenous β-NAD mimics the effects of the enteric inhibitory neurotransmitter. Responses to β-NAD and inhibitory junction potentials are blocked by the P2Y1-selective antagonist, MRS2179, and the nonselective P2 receptor antagonists, pyridoxal phosphate 6-azophenyl-2',4'-disulfonic acid and suramin. Responses to ATP are not blocked by these P2Y receptor inhibitors. The expression of CD38 in gastrointestinal muscles, and specifically in interstitial cells of Cajal, provides a means of transmitter disposal after stimulation. β-NAD meets the traditional criteria for a neurotransmitter that contributes to enteric inhibitory regulation of visceral smooth muscles.