Me. Klingensmith et al., EVIDENCE FOR CL--INDEPENDENT HCO3- TRANSPORT IN BASOLATERAL MEMBRANESOF NECTURUS OXYNTOPEPTIC CELLS, American journal of physiology: Gastrointestinal and liver physiology, 34(6), 1996, pp. 1096-1103
Luminal H+ secretion by gastric mucosa is accompanied by basolateral H
CO3- release. A basolateral Cl-/HCO3- exchanger is known to mediate HC
O3- extrusion from oxyntopeptic cells during resting and secretagogue-
induced apical HCl secretion. From recent work, we hypothesized that t
here might be a Cl--independent pathway for basolateral HCO3- exit in
Necturus oxyntopeptic cells. In this study, we used a fluorescent pH i
ndicator 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein] to evaluat
e Cl--independent HCO3- transport across the basolateral membranes of
intact oxyntopeptic cells. Removal of serosal Cl- increased intracellu
lar pH (pH(i)) (7.05 to 7.25), consistent with Cl--dependent HCO3- ext
rusion. Removal of serosal Na+ in the absence of Cl- resulted in signi
ficant acidification of pH(i) (7.10 to 6.89), but studies involving am
iloride, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), and
0 O3--N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered sol
utions suggest that Na+-dependent changes in pH(i) are due to Na+/H+ e
xchange. Our studies demonstrate a marked concentration-dependent alka
linization when tissues are exposed to increases in serosal K+. A subs
tantial part of this alkalinization in response to increases in serosa
l K+ (pH(i) 7.00 to 7.46) appears to be a HCO3- exit pathway that is i
ndependent of both Na+ and Cl-, unaffected by bumetanide or amiloride,
but sensitive to DIDS. We propose the presence of a Cl-- and Na+-inde
pendent K+-dependent HCO3- cotransporter in Necturus oxyntopeptic cell
basolateral membranes.