title: Beta-nicotinamide adenine dinucleotide is an inhibitory neurotransmitter in visceral smooth muscle.
abstract: 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 beta-nicotinamide adenine dinucleotide (beta-NAD), an inhibitory neurotransmitter candidate, is released by stimulation of enteric nerves in gastrointestinal muscles, and the pharmacological profile of beta-NAD mimics the endogenous neurotransmitter better than ATP. Levels of beta-NAD in superfusates of muscles after nerve stimulation exceed ATP by at least 30-fold; unlike ATP, the release of beta-NAD depends on the frequency of nerve stimulation. beta-NAD is released from enteric neurons, and release was blocked by tetrodotoxin or omega-conotoxin GVIA. beta-NAD is an agonist for P2Y1 receptors, as demonstrated by receptor-mediated responses in HEK293 cells expressing P2Y1 receptors. Exogenous beta-NAD mimics the effects of the enteric inhibitory neurotransmitter. Responses to beta-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. beta-NAD meets the traditional criteria for a neurotransmitter that contributes to enteric inhibitory regulation of visceral smooth muscles.
authors.affiliation: Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV 89557, USA.
authors.forename: Violeta N
authors.initials: VN
authors.lastname: Mutafova-Yambolieva
authors.forename: Sung Jin
authors.initials: SJ
authors.lastname: Hwang
authors.forename: Xuemei
authors.initials: X
authors.lastname: Hao
authors.forename: Hui
authors.initials: H
authors.lastname: Chen
authors.forename: Michael X
authors.initials: MX
authors.lastname: Zhu
authors.forename: Jackie D
authors.initials: JD
authors.lastname: Wood
authors.forename: Sean M
authors.initials: SM
authors.lastname: Ward
authors.forename: Kenton M
authors.initials: KM
authors.lastname: Sanders
mesh_terms: D000244:Adenosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D004558:Electric Stimulation; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D008810:Mice, Inbred C57BL; D009130:Muscle, Smooth / Q000187:drug effects / Q000294:innervation*; D009243:NAD / Q000502:physiology*; D018377:Neurotransmitter Agents / Q000502:physiology*; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2 / Q000235:genetics / Q000502:physiology; D058472:Receptors, Purinergic P2Y1; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
chemical_list: C111914:N(6)-methyl-2'-deoxyadenosine 3',5'-diphosphate; D018377:Neurotransmitter Agents; C546382:P2RY1 protein, human; C546383:P2ry1 protein, mouse; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; D058472:Receptors, Purinergic P2Y1; D011994:Recombinant Proteins; D009243:NAD; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate