Chloride-dependent bicarbonate secretion in the mouse large intestine

Abstract

The gastrointestinal HCO − 3 secretion functions to limit the mucosal acid damage due to HCl secreted in the stomach or organic acids produced in the large intestine. We studied HCO − 3 secretion in the mouse large intestine with isolated tissues mounted in chambers by using pH stat method. Addition of Cl − to the mucosal side caused an increase in HCO − 3 secretion in the cecum and distal colon but had little, if any, effect in the proximal colon. In agreement with this, mucosal surface pH was higher in the cecum and distal colon than in the proximal colon. The Cl

Segregation of Na/H exchanger-3 and Cl/HCO3exchanger SLC26A3 (DRA) in rodent cecum and colon

“…Just centimeters downstream, after 20% colon length, pH ms increased sharply and remained alkaline (pH ϳ7.5) throughout the mid and distal colon (40 -90% colon). Similar juxtamucosal pH profiles along the cecocolonic axis of mice have been reported (46). Our results are consistent with recent evidence that the cecum and distal colon, but not the proximal colon, secrete net base equivalents (46).…”

“…Similar juxtamucosal pH profiles along the cecocolonic axis of mice have been reported (46). Our results are consistent with recent evidence that the cecum and distal colon, but not the proximal colon, secrete net base equivalents (46). It is evident that the cecocolonic profiles of pH ms (Fig.…”

“…In addition to energetically limiting the extent of Ϫ exchange, the existence of a stable alkaline layer along the surface of the cecum and distal colon is expected to reduce the proportion of unprotonated SCFAs available for apical transit via nonionic diffusion (12). On the basis of studies of isolated mouse cecum, this alkaline layer appears attributable to an apical SCFA/HCO 3 exchange process that is independent of MCT1 (47) and an apical Cl/HCO 3 exchange process that is defective in DRA knockout mice (46,79). In the rodent cecum, SCFA/HCO 3 exchange and Cl/HCO 3 exchange are evidently not coupled to NHE3 or NHE2 activities, as they are in the midcolon (6), since Na ϩ absorptive capacity is relatively low (72) and NHE3 protein expression is negligible (Figs.…”

Secretagogues stimulate electrogenic HCO3–secretion in the ileum of the brushtail possum,Trichosurus vulpecula:evidence for the role of a Na+/HCO3– cotransporter

“…In the absence of significant electrogenic secretion in the hindgut of the possum (Butt et al, 2002b), the electrogenic HCO 3 -secretion by the ileum may be an important means of not only regulating the luminal pH, but also ensuring a sufficient volume of fluid for microbial growth. By contrast, the proximal colon of eutherian hindgut fermenters is capable of both fluid and HCO 3 -secretion (Clauss, 1986;Sullivan, 1986;Hyun et al, 1994;Kawamata et al, 2006). Therefore, it may not be necessary to deliver similar volumes of HCO 3 --rich fluid from the ileum.…”

News from the End of the Gut-How the Highly Segmental Pattern of Colonic HCO3- Transport Relates to Absorptive Function and Mucosal Integrity

“…103,104) Since there is no coupling with NHE2 or NHE3, which is not significantly expressed in this segment, 38) net HCO 3 Ϫ secretion occurs, which influences the mucosal surface microclimate (3.5) and possibly also bulk stool pH. This is likely to promote the nonionic diffusion of unprotonated SCFAs 105) (3.2), which are produced at high concentrations in the cecum by bacterial fermentation together with CO 2 from indigestible polysaccharides, and to balance the resulting high acid load in the cecal lumen.…”