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Maintenance and regulation of the pH microclimate at the luminal surface of the distal colon of guinea‐pig
Author(s) -
Genz AnneKatrin,
Engelhardt Wolfgang,
Busche Roger
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.0507t.x
Subject(s) - guinea pig , microclimate , chemistry , distal colon , biophysics , anatomy , biology , endocrinology , ecology
1 The fluorescent dye 5‐ N ‐hexadecanoyl‐aminofluorescein (HAF) was used to study the mechanisms involved in maintaining a relatively constant luminal surface pH (pH s ) 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 pH s changed only in the range 7.54‐6.98. 4 In the absence of bicarbonate pH s almost followed changes of bulk luminal pH. In the presence of bicarbonate there was a decrease in pH s after removal of chloride from the luminal side and an increase in pH s after addition of butyrate to the luminal solution. This suggests the involvement of a bicarbonate‐anion exchange in bicarbonate secretion: a Cl − ‐HCO 3 − as well as a short‐chain fatty acid − ‐HCO 3 − exchange. 5 The apical K + ‐H + ‐ATPase in the distal colon of guinea‐pig has little influence on pH s 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.