Contrary effects of the gut metabolites deoxycholate and butyrate on the acetylcholine-evoked calcium response in an enteroendocrine cell model

The interaction of nutrients and bacterial-derived products and their enteroendocrine effects are still enigmatic. We used the human enteroendocrine tumour cell line P-STS isolated from the terminal ileum as cellular sentinel. In this model, P-STS cells react to acetylcholine or histamine with an increase in intracellular calcium mediated by T-type voltage-gated calcium channels followed by serotonin secretion. Incubation with the secondary bile acid deoxycholate inhibited the calcium response to acetylcholine but not to histamine. No response to other nutrients or bacterial products tested (i.e. palmitate, lactate, acetate, proprionate, butyrate, the OR51E1 ligand isovalerate and the HCA2 ligand β-hydroxybutyrate) could be observed. The bile acid receptor TGR5 agonist CCDC did not inhibit the acetylcholine-induced calcium response, and the free fatty acid receptor 2 agonist 4-CMTB had no enhancing effect on the calcium response to acetylcholine. Only butyrate had an enhancing effect on the calcium response in P-STS cells when added for short-time pre-incubation before challenge with acetylcholine. From our data we propose i) an inhibitory effect of deoxycholate at the muscarinic acetylcholine receptor M3 without involvement of TGR5, and that ii) high butyrate concentrations derived from bacterial metabolism of carbohydrates might increase intestinal release of serotonin and potentially also other gut hormones and satiety-inducing peptides independently of known butyrate receptors, thereby influencing intestinal motility and ion secretion.