Adenosine 5′‐diphosphate‐ribose is a neural regulator in primate and murine large intestine along with β‐NAD+

Abstract

Adenosine 5′-triphosphate (ATP) has long been considered to be the purine inhibitory neurotransmitter in gastrointestinal (GI) muscles, but recent studies indicate that another purine nucleotide, β-nicotinamide adenine dinucleotide (β-NAD(+)), meets pre- and postsynaptic criteria for a neurotransmitter better than ATP in primate and murine colons. Using a small-volume superfusion assay and HPLC with fluorescence detection and intracellular microelectrode techniques we compared β-NAD(+) and ATP metabolism and postjunctional effects of the primary extracellular metabolites of β-NAD(+) and ATP, namely ADP-ribose (ADPR) and ADP in colonic muscles from cynomolgus monkeys and wild-type (CD38(+/+)) and CD38(−/−) mice. ADPR and ADP caused membrane hyperpolarization that, like nerve-evoked inhibitory junctional potentials (IJPs), were inhibited by apamin. IJPs and hyperpolarization responses to ADPR, but not ADP, were inhibited by the P2Y1 receptor antagonist (1R,2S,4S,5S)-4-[2-iodo-6-(methylamino)-9H-purin-9-yl]-2-(phosphonooxy)bicyclo[3.1.0]hexane-1-methanol dihydrogen phosphate ester tetraammonium salt (MRS2500). Degradation of β-NAD(+) and ADPR was greater per unit mass in muscles containing only nerve processes than in muscles also containing myenteric ganglia. Thus, mechanisms for generation of ADPR from β-NAD(+) and for termination of the action of ADPR are likely to be present near sites of neurotransmitter release. Degradation of β-NAD(+) to ADPR and other metabolites appears to be mediated by pathways besides CD38, the main NAD-glycohydrolase in mammals. Degradation of β-NAD(+) and ATP were equal in colon. ADPR like its precursor, β-NAD(+), mimicked the effects of the endogenous purine neurotransmitter in primate and murine colons. Taken together, our observations support a novel hypothesis in which multiple purines contribute to enteric inhibitory regulation of gastrointestinal motility.