BQ788 reveals glial ETB receptor modulation of neuronal cholinergic and nitrergic pathways to inhibit intestinal motility: Linked to postoperative ileus

Background and PurposeET-1 signalling modulates intestinal motility and inflammation, but the role of ET-1/ETB receptor signalling is poorly understood. Enteric glia modulate normal motility and inflammation. We investigated whether glial ETB signalling regulates neural-motor pathways of intestinal motility and inflammation. Experimental ApproachWe studied ETB signalling using: ETB drugs (ET-1, SaTX, BQ788), activity-dependent stimulation of neurons (high K+-depolarization, EFS), gliotoxins, Tg (Ednrb-EGFP)EP59Gsat/Mmucd mice, cell-specific mRNA in Sox10(CreERT2);Rpl22-HAflx or ChAT(Cre);Rpl22-HAflx mice, Sox10(CreERT2)::GCaMP5g-tdT, Wnt1(Cre2)::GCaMP5g-tdT mice, muscle tension recordings, fluid-induced peristalsis, ET-1 expression, qPCR, western blots, 3-D LSM-immunofluorescence co-labelling studies in LMMP-CM and a postoperative ileus (POI) model of intestinal inflammation. Key ResultsIn the muscularis externa ETB receptor is expressed exclusively in glia. ET-1 is expressed in RiboTag (ChAT)-neurons, isolated ganglia and intra-ganglionic varicose-nerve fibres co-labelled with peripherin or SP. ET-1 release provides activity-dependent glial ETB receptor modulation of Ca2+ waves in neural evoked glial responses. BQ788 reveals amplification of glial and neuronal Ca2+ responses and excitatory cholinergic contractions, sensitive to L-NAME. Gliotoxins disrupt SaTX-induced glial-Ca2+ waves and prevent BQ788 amplification of contractions. The ETB receptor is linked to inhibition of contractions and peristalsis. Inflammation causes glial ETB up-regulation, SaTX-hypersensitivity and glial amplification of ETB signalling. In vivo BQ788 (i.p., 1 mg & BULL;kg(-1)) attenuates intestinal inflammation in POI. Conclusion and ImplicationsEnteric glial ET-1/ETB signalling provides dual modulation of neural-motor circuits to inhibit motility. It inhibits excitatory cholinergic and stimulates inhibitory nitrergic motor pathways. Amplification of glial ETB receptors is linked to muscularis externa inflammation and possibly pathogenic mechanisms of POI.