EVIDENCE FOR CL--INDEPENDENT HCO3- TRANSPORT IN BASOLATERAL MEMBRANESOF NECTURUS OXYNTOPEPTIC CELLS

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.