Non‐neuronal release of ACh plays a key role in secretory response to luminal propionate in rat colon

Abstract

Non-technical summary ACh is the best characterized neurotransmitter that is synthesized in cholinergic neurons in the brain and gut wall. In the gut, acetylcholine is released from the nerve endings in response to luminal stimuli and regulates the movement of gut contents via stimulating muscle contraction and epithelial ion secretion. We show that acetylcholine is synthesized in colonic epithelial cells and released on the serosal side by luminal chemical stimulation of the short chain fatty acid propionate and causes chloride secretion. These results suggest that non-neuronal release of acetylcholine in response to luminal stimuli plays a role in colonic chloride secretion.Abstract Colonic chloride secretion is induced by chemical stimuli via the enteric nervous reflex. We have previously demonstrated that propionate stimulates chloride secretion via sensory and cholinergic systems of the mucosa in rat distal colon. In this study, we demonstrate non-neuronal release of ACh in the secretory response to propionate using an Ussing chamber. Mucosa preparations from the colon, not including the myenteric and submucosal plexuses, were used. Luminal addition of propionate and serosal addition of ACh caused biphasic changes in short-circuit current (I sc ). TTX (1 μM) had no effects, while atropine (10 μM) significantly inhibited the I sc response to propionate and abolished that to ACh. In response to luminal propionate stimulation, ACh was released into the serosal fluid. A linear relationship was observed between the maximal increase in I sc and the amounts of ACh released 5 min after propionate stimulation. This ACh release induced by propionate was not affected by atropine and bumetanide, although both drugs significantly reduced the I sc responses to propionate. Luminal addition of 3-chloropropionate, an inactive analogue of propionate, abolished both ACh release and I sc response produced by propionate. RT-PCR analysis indicated that isolated crypt cells from the distal colon expressed an enzyme of ACh synthesis (ChAT) and transporters of organic cation (OCTs), but not neuronal CHT1 and VAChT. The isolated crypt cells contained comparable amounts of ACh to the residual muscle tissues including nerve plexuses. In conclusion, the non-neuronal release of ACh from colonocytes coupled with propionate stimulation plays a key role in chloride secretion, via the paracrine action of ACh on muscarinic receptors of colonocytes. Abbreviations ChAT, choline acetyltransferase; CHT1, high affinity choline transporter; OCT, organic cation transporter; SCFA, short chain fatty acid; VAChT, vesicular acetylcholine transporter.

Activation of TRPA1 by luminal stimuli induces EP4-mediated anion secretion in human and rat colon

“…Recently, Yajima and colleagues (52) reported that nonneural ACh is released by colonic mucosa and is involved in anion secretion response to luminal propionate. To investigate whether an AITC-evoked increase in I sc was mediated by nonneural ACh, the muscarinic receptor antagonist atropine (10 Ϫ5 M) was added to the serosal bathing solution 15 min before the application of AITC (10 Ϫ4 M).…”

“…Expression of TRPA1 in rat colonic epithelia. Crypt isolation is an efficient way to prevent contamination of subepithelial cells and nerves in lamina propria (52). To confirm TRPA1 expression in epithelial cells, RT-PCR was performed using colorectal crypts compared with the residual tissues; i.e., submucosa and muscle layers containing enteric neurons.…”

The cholinergic system in rat testis is of non-neuronal origin

“…This is supported by the fact that the molecule responsible for storage of ACh, SLC18A3, could not be detected in the germ cell population. This is similar to human and murine leukocytes and crypt cells in the distal rat colon, which also do not express SLC18A3, but contains or synthesises ACh (Kawashima & Fujii 2000, Yajima et al 2010. In addition, vascular endothelial cells, TM and Sertoli cells could also be a potential source of endogenous ACh.…”

Chemosense for Luminal Environment in the Large Intestine

“…23) Most recently, luminal propionate was found to induce ACh release from colonic epithelial cells themselves. 24) This propionate-and butyrate-induced Cl -secretion was also observed in the distal small intestine, 25) but not in the proximal colon. 23) Additionally, there are species diŠerences in the secretory eŠect of SCFAs.…”