Abstract
OBJECTIVE: Regulation of colonic motility depends upon the integrity of enteric inhibitory neurotransmission mediated by nitric oxide (NO), multiple purine neurotransmitters, and neuropeptides. Intramuscular interstitial cells of Cajal (ICC-IM) and platelet-derived growth factor receptor α-positive (PDGFRα(+)) cells are involved in generating responses to NO and purine neurotransmitters, respectively. Previous studies have reported reduced nitrergic neurotransmission and upregulation of purinergic signaling in gastrointestinal muscles from Kit(W)/Kit(W-v) (W/W(v)) mice that display viable lesions in ICC-IM along the GI tract, including the colon. However, contributions of NO to these phenotypes have not been evaluated. The present study was undertaken to determine whether neural release of purines is altered in colons from W/W(v) mice and to investigate the role of NO in these mechanisms. METHODS: We utilized small-chamber superfusion assays and high-performance liquid chromatography with fluorescence detection (HPLC-FLD) to measure the spontaneous and electrical field stimulation (EFS)-evoked release of nicotinamide adenine dinucleotide (NAD(+))/ADP-ribose, uridine adenosine tetraphosphate (Up4A), adenosine 5'-triphosphate (ATP), and metabolites from the tunica muscularis of human and murine colons, and we tested drugs that modulate NO levels or blocked NO receptors. RESULTS: NO inhibited EFS-evoked release of NAD(+)/ADP-ribose, Up4A, and ATP in the colon via presynaptic neuromodulation. Colons from W/W(v), Nos1(−/−,) and Prkg1(−/−) mice displayed augmented neural release of purines that was likely due to altered nitrergic neuromodulation. Colons from W/W(v) mice demonstrated decreased nitrergic and increased purinergic relaxations in response to nerve stimulation. Extracellular purine metabolism was not altered in W/W(v) colons. W/W(v) mouse colons also demonstrated reduced Nos1 expression and reduced NO release, suggesting that NO available for prejunctional inhibition of purine release is likely reduced in these tissues. CONCLUSIONS: NO mediates inhibition of purine release that may act to prevent “over-inhibition” of colonic muscles during increased motor neuron activation. Enhanced purinergic neurotransmission may compensate for the loss of nitrergic neurotransmission in muscles with partial loss of ICC. The interactions between nitrergic and purinergic neurotransmission in the colon provides novel insight into the role of neurotransmitters and effector cells in the neural regulation of gastrointestinal motility. FUNDING SOURCE(S): a grant from the National Institutes of Health, USA, DK 41315