AJP - Gastrointestinal and Liver Physiology, Vol 271, Issue 6 1096-G1103, Copyright © 1996 by American Physiological Society
Evidence for Cl(-)-independent HCO3- transport in basolateral membranes of Necturus oxyntopeptic cells
M. E. Klingensmith, R. R. Cima, A. E. Gadacz and D. I. Soybel
Department of Surgery, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
Luminal H+ secretion by gastric mucosa is accompanied by basolateral HCO3-
release. A basolateral Cl-/HCO3- exchanger is known to mediate HCO3-
extrusion from oxyntopeptic cells during resting and secretagogue-induced
apical HCl secretion. From recent work, we hypothesized that there might be
a Cl(-)-independent pathway for basolateral HCO3- exit in Necturus
oxyntopeptic cells. In this study, we used a fluorescent pH indicator
[2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein] to evaluate
Cl(-)-independent HCO3- transport across the basolateral membranes of
intact oxyntopeptic cells. Removal of serosal Cl- increased intracellular
pH (pHi) (7.05 to 7.25), consistent with Cl(-)-dependent HCO3- extrusion.
Removal of serosal Na+ in the absence of Cl- resulted in significant
acidification of pHi (7.10 to 6.89), but studies involving amiloride,
4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), and 0
HCO3(-)-N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered
solutions suggest that Na(+)-dependent changes in pHi are due to Na+/H+
exchange. Our studies demonstrate a marked concentration-dependent
alkalinization when tissues are exposed to increases in serosal K+. A
substantial part of this alkalinization in response to increases in serosal
K+ (pHi 7.00 to 7.46) appears to be a HCO3- exit pathway that is
independent of both Na+ and Cl-, unaffected by bumetanide or amiloride, but
sensitive to DIDS. We propose the presence of a Cl(-)- and
Na(+)-independent K(+)-dependent HCO3- cotransporter in Necturus
oxyntopeptic cell basolateral membranes.
