Fructooligosaccharides slow colonic motility and activate myenteric neurons via calcium sensing and 5-HT₃ receptors in the proximal colon

Calcium-sensing receptors (CaSR) regulate a variety of functions in the gastrointestinal tract. Recently, prebiotic-independent effects of fructooligosaccharides (FOS) on epithelial barrier function were found to be mediated by CaSR. Here, we tested the hypothesis that FOS acts via the CaSR to regulate colonic motility and neuronal activity in the enteric nervous system. Using immunohistochemistry, we determined that CaSR were localized on the colonic epithelium of the mouse proximal colon and that a small proportion of enterochromaffin cells coexpress CaSR. We demonstrated that intraluminal administration of FOS slows colonic motility in vivo in male and female mice, an effect that is mediated by both CaSR and 5-HT₃ receptors. We assessed neuronal activity in response to luminally perfused FOS in intact segments of the proximal colon from male and female mice expressing a genetically encoded fluorescent calcium reporter in intrinsic primary afferent neurons (Calb1-GCaMP6 mice) or in all enteric neurons (Wnt1-GCaMP6 mice) using live cell confocal imaging. In both Calb1-GCaMP6 mice and Wnt1-GCaMP6 mice, intraluminal FOS perfusion induced a sustained elevation of intracellular Ca²⁺ in neurons of the myenteric plexus. This effect was sensitive to tetrodotoxin and mediated by CaSR and 5-HT₃ receptors. Serosal application of FOS was without effect. Our results demonstrate that FOS acts acutely to slow colonic motility in vivo and activates the enteric nervous system via CaSR and 5-HT₃ receptors.<b>NEW & NOTEWORTHY</b> Calcium-sensing receptors regulate a variety of functions in the gastrointestinal tract. Here, we demonstrate a novel action of fructooligosaccharides to regulate colonic motility in vivo and activate the enteric nervous system. These effects are mediated by calcium-sensing and 5-HT₃ receptors.