title: Maintenance and regulation of the pH microclimate at the luminal surface of the distal colon of guinea-pig.
abstract: 1. The fluorescent dye 5-N-hexadecanoyl-aminofluorescein (HAF) was used to study the mechanisms involved in maintaining a relatively constant luminal surface pH (pHs) in the distal colon of the guinea-pig. The fatty acyl chain of the HAF molecule inserts into the apical membrane of epithelial cells. This allows a continuous measurement of the surface pH for several hours. 2. The localization of HAF was confirmed by confocal laser-scanning microscopy and by using monoclonal antibodies against fluorescein. The insertion of HAF into the apical membrane of the colonocytes did not change the transepithelial conductance or the short-circuit current of the epithelium. 3. With the HAF method a pH microclimate was confirmed at the colonic surface. Although the pH of the bulk luminal solution was decreased in bicarbonate-containing solution from 7.4 to 6.4 the pHs changed only in the range 7.54-6.98. 4. In the absence of bicarbonate pHs almost followed changes of bulk luminal pH. In the presence of bicarbonate there was a decrease in pHs after removal of chloride from the luminal side and an increase in pHs after addition of butyrate to the luminal solution. This suggests the involvement of a bicarbonate-anion exchange in bicarbonate secretion: a Cl--HCO3- as well as a short-chain fatty acid--HCO3- exchange. 5. The apical K+-H+-ATPase in the distal colon of guinea-pig has little influence on pHs in the presence of physiological buffer concentrations. 6. Our findings indicate that bicarbonate plays a major role in maintaining the pH microclimate at the colonic surface.
authors.affiliation: Department of Physiology, School of Veterinary Medicine, D-30157 Hannover, Germany.
authors.forename: A K
authors.initials: AK
authors.lastname: Genz
authors.forename: W
authors.initials: W
authors.lastname: v Engelhardt
authors.forename: R
authors.initials: R
authors.lastname: Busche
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001639:Bicarbonates / Q000378:metabolism; D002138:Calibration; D002462:Cell Membrane / Q000201:enzymology; D003106:Colon / Q000378:metabolism*; D005232:Fatty Acids, Volatile / Q000378:metabolism; D005452:Fluoresceins / Q000493:pharmacokinetics; D005453:Fluorescence; D005456:Fluorescent Dyes / Q000493:pharmacokinetics; D005470:Fluorometry; D006168:Guinea Pigs; D017506:H(+)-K(+)-Exchanging ATPase / Q000378:metabolism; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000378:metabolism*; D017136:Ion Transport / Q000502:physiology; D008297:Male; D018613:Microscopy, Confocal
chemical_list: D000911:Antibodies, Monoclonal; D001639:Bicarbonates; D005232:Fatty Acids, Volatile; D005452:Fluoresceins; D005456:Fluorescent Dyes; C058719:(hexadecanoyl)aminofluorescein; D006859:Hydrogen; D017506:H(+)-K(+)-Exchanging ATPase