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

Abstract

A number of transport mechanisms in the colonic epithelium contribute to HCO 3 ؊ ؊ movement across the apical and basolateral membranes, but this ion has been largely regarded as a by-product of the transport functions it is involved in, such as NaCl-or short chain fatty acid (SCFA) absorption. However, emerging data points to several specific roles of HCO 3 ؊ ؊ for colonic epithelial physiology, including pH control in the colonic surface microenvironment, which is important for transport-and immune functions, as well as the secretion and the rheological properties of the mucus gel. Furthermore, recent studies have demonstrated that colonic HCO 3 ؊ ؊ transporters are expressed in a highly segmental as well as species-specific manner. This review summarizes recently gathered information on the functional anatomy of the colon, the roles of HCO 3 ؊ ؊ in the colonic epithelium, colonic mucosal integrity, and the expression and function of HCO 3 ؊ ؊ transporting mechanisms in health and disease.

Chronic metabolic acidosis reduces urinary oxalate excretion and promotes intestinal oxalate secretion in the rat

“…G t = 10.62 ± 0.75 (n = 24, 4 days) and 11.33 ± 0.96 (n = 22, control) potassium secretion [28,43,44]. We can now extend this to oxalate, a substrate of the same Cl − /HCO 3 − anion exchangers responsible for Cl − absorption and HCO 3 − secretion by the large intestine [45]. In the rat distal colon, DRA (Down-Regulated in Adenoma; SLC26a3) and AE1 (Anion Exchanger 1; SLC4a1) function as respective apical Cl − / OH − and Cl − /HCO 3 − exchangers [46,47]; however, the specific transporters responsible for oxalate transport by the rat large intestine have not been determined.…”

Extracellular pH Regulates Zinc Signaling via an Asp Residue of the Zinc-sensing Receptor (ZnR/GPR39)

“…Interestingly, a Ca 2ϩ -sensing receptor, CaSR, is a G-protein-coupled receptor that is found on the basolateral side of colonocytes and is tuned to sense alkaline pH changes monitored on this side of the cells (27,37,38). It will be of interest to determine if the concerted activity of the CaSR and ZnR shape the response of colonocytes to pH and regulate short chain fatty acid transport and bicarbonate secretion (39). In the gastric mucosa Zn 2ϩ is indeed involved in regulation of acid secretion via a Ca 2ϩ -dependent mechanism (40).…”

Establishment and Characterization of an SV40 Large T Antigen-Transduced Porcine Colonic Epithelial Cell Line

“…Thus, we expect PoCo83-3 to provide new perspectives in transport physiological studies. However, with respect to species-specific, segmental-and differentiation-dependent differences [Bachmann and Seidler, 2011], a more detailed characterization concerning the expression pattern and functionality of these transport proteins at the protein level in PoCo83-3 cells is necessary.…”