Low carbon dioxide permeability of the apical epithelial membrane of guinea‐pig colon

Abstract

We have investigated the apical membrane permeability for CO 2 of intact epithelia of proximal and distal colon of the guinea pig. The method used was the mass spectrometric 18 O-exchange technique previously described. In a first step, we determined the intraepithelial carbonic anhydrase (CA) activity by studying vital isolated colonocytes before and after lysis with Triton X-100. Intraepithelial CA activity was found to be 41 000 and 900 for proximal and distal colon, respectively. Then 18 O-exchange measurements were done with stripped intact epithelial layers, which on their apical side were exposed to the reaction solution containing 18 O-labelled CO 2 and HCO 3 − . The mass spectrometric signals in these measurements are determined by the intracellular epithelial CA activity, and by the apical membrane permeabilities for CO 2 and HCO 3 − , P CO 2 and P HCO 3 . From the signals, we calculated the two permeabilities while inserting the CA activities obtained from isolated colonocytes. From layers of intact colon epithelium, the apical P CO 2 was determined to be 1.5 × 10 −3 cm s −1 for proximal and 0.77 × 10 −3 cm s −1 for distal colon. These values are ≥200 times lower than the P CO 2 of the human red cell membrane as studied with the same technique (0.3 cm s −1 ). We conclude that the apical membrane offers a significant resistance towards CO 2 diffusion, which implies that a major drop in CO 2 partial pressure (pCO 2 ) will occur across the apical membrane when luminal pCO 2 is higher than basolateral or capillary pCO 2 . In view of the very high pCO 2 that can occur in the colonic lumen, this property of the apical membrane constitutes a significant protection of the cell against the high acid load associated with high pCO 2 .

The Mechanistic Basis of Internal Conductance: A Theoretical Analysis of Mesophyll Cell Photosynthesis and CO2 Diffusion

“…However, the lower limit for HCO 3 2 permeability through artificial phospholipid membranes was estimated to be around 4.3 3 10 28 m s 21 (Norris and Powell, 1992). Heber and Purczeld (1978) This value is similar to the maximum HCO 3 2 permeability predicted for a simple lipid bilayer by Gutknecht et al (1977) Endeward and Gros, 2005). We took a HCO 3 2 membrane permeability of 5 3 10 27 m s 21 as a starting point for the simulations (Table I) and tested for the effect of variation in this parameter (Figs.…”

CO2 Permeability of Rat Hepatocytes and Relation of CO2 Permeability to CO2 Production

“…It was attached to the high vacuum of the mass spectrometer via the previously published inlet system [1, 8, 9]. This chamber had a water-jacket that kept the solutions at 37°C, and contained a stirrer that mixed the content continuously.…”

“…Membranes from various cells and organelles have shown P CO2 values varying between 0.001 cm/s for the apical membrane of colon ephitelium [1] to 0.3 cm/s for the mitochondrial membrane [2]. These differences in P CO2 have been shown to be associated with two main factors: the cholesterol content of the membrane [3] and the presence/absence of CO 2 channels in the membrane [3-5].…”

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

“…35,99) However, CO 2 permeability through the apical membrane of guinea pig colon was relatively low. 100) A recent study has correlated mucosal surface pH with the apical expression of DRA and NHE3 along the ileocolon of the rat. 38) Mucosal surface pH was low in the proximal colon and rose towards the mid colon, demonstrating that a high surface pH correlated with DRA expression in the colon.…”

“…Endeward and Gros have reported a 40 times higher intracellular carbonic anhydrase activity in proximal than in distal colon of the guinea pig, which was thus greater than in the human red cell. 100) CA could likely propagate intracellular H ϩ and HCO 3 Ϫ generation, which is then extruded by the respective exchanger. However, in human proximal colonic apical membrane vesicles, an outwardly directed HCO 3 Ϫ gradient stimulated 36 Cl uptake, compatible with Cl…”