Na+-H+ and Cl(-)-OH-(HCO3-) exchange in gastric glands

Abstract

The pH-sensitive, fluorescent, cytoplasmic-trapped dye 2,7-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF) has been used to measure intracellular (pHi) and pH electrode to measure extracellular pH (pHo) in suspensions of gastric glands isolated from rabbit stomachs. The fluorescence of BCECF-loaded glands was calibrated in terms of pHi by equilibrating pHo and pHi using ionophores or digitonin and titrating pHo to different values. An APPENDIX is included that covers details of dye calibration and interpretation of fluorescence signals. Glands incubated in NaCl Ringer solution had pHi 7.11. Na+-free Ringer solution caused pHi to decrease reversibly to 6.80. Na+-dependent alkalinization of pHi followed a similar time course to the acidification of pHo. These changes were blocked by 1 mM amiloride. When gland cells were acidified (using two different techniques) realkalinization was completely Na+ dependent but was independent of the presence of Cl-; also, neither high extracellular K+ concentration ([K+]o) nor high [K+]o plus 10(-5) M valinomycin affected the rates of Na+-dependent alkalinization. A neutral Na+-H+ exchanger was implicated. Glands also exhibited Cl(-)-dependent changes of pHi that were blocked by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (2 X 10(-4) M). A Cl(-)-OH-(HCO3-) exchanger was indicated. Other studies showed that intracellular buffering capacity was approximately 45 mM (pH-1) and that the apparent proton conductance of gland cell membranes was small.