BQ788 Reveals Glial ETB_R Modulation of Neuronal Cholinergic and Nitrergic Pathways to Inhibit Intestinal Motility: ETB_R Signaling is Linked to POI

Br J Pharmacol. 2023 May 17. doi: 10.1111/bph.16145. Online ahead of print.

ABSTRACT

BACKGROUND AND PURPOSE: ET-1 signaling modulates intestinal motility and inflammation, but the role of ET-1/ETB_R signaling is poorly understood. Enteric glia modulate normal motility and inflammation. We investigated whether glial ETB_R signaling is a mechanism regulating neural-motor pathways of intestinal motility and inflammation.

EXPERIMENTAL APPROACH: We studied ETB_R signaling using: ETB_R 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 Sox10CreERT2; Rpl22-HAflx or ChATCre; 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-labeling studies in LMMP-CM and a POI model of intestinal inflammation (P<0.01 is significant).

KEY RESULTS: In the muscularis externa ETB_R is expressed exclusively in glia. ET-1 is expressed in RiboTag (ChAT)-neurons, isolated ganglia and intra-ganglionic varicose-nerve fibers co-labeled with peripherin or SP. Pharmacological analysis of neural evoked glial responses indicates that ET-1 release provides activity-dependent glial ETB_R modulation of Ca²⁺ waves. BQ788 reveals amplification of glial and neuronal Ca²⁺ responses and excitatory cholinergic contractions. The BQ788 effect is sensitive to L-NAME. Gliotoxins disrupt SaTX-induced glial-Ca²⁺ waves and prevent BQ788 amplification of contractions. ETB_R is linked to inhibition of contractions and peristalsis. Inflammation causes glial ETB_R upregulation, SaTX-hypersensitivity and glial amplification of ETB_R signaling. In vivo BQ788 (i.p.,1mg/Kg) attenuates intestinal inflammation in POI.

CONCLUSION AND IMPLICATIONS: Enteric glial ET-1/ETB_R signaling provides dual modulation of neural-motor circuits to inhibit motility - It inhibits excitatory cholinergic neural-motor pathways and stimulates inhibitory nitrergic motor pathways. Amplification of glial ETB_R is linked to muscularis externa inflammation and possibly pathogenic mechanisms of postoperative ileus.

PMID:37198101 | DOI:10.1111/bph.16145