pHi and HCO3- dependence of proton extrusion and Cl (-) -base exchange rates in isolated rabbit parietal cells
Seidler, U.; Hübner, M.; Roithmaier, S.; Classen, M.
American Journal of Physiology 266(5 Pt 1): G759-G766
1994
ISSN/ISBN: 0002-9513 PMID: 8203522 Document Number: 436582
In many cell types, the regulation of intracellular pH (pH-i) is different in the presence vs. absence of HCO-3-. We investigated the pH-i and HCO-3- dependence of proton extrusion and anion exchange rates in isolated rabbit parietal cells loaded with the pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)carboxyfluorescein (BCECF). In Cl--depleted parietal cells, the dependence of maximal proton efflux rate on pH-i showed a strong inverse correlation but was identical in the presence and absence of HCO-3-. Amiloride and Na+ removal inhibited proton extrusion rates to a similar degree with or without HCO-3-, whereas 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) had no effect. This suggests that a Na+-H+ exchanger is the major acid extrusion ion transporter under these experimental conditions. In Cl--containing cells, there was also some Na+-independent, extracellular HCO-3-- and intracellular Cl--dependent, DIDS-inhibitable pH-i recovery from an acid load, most likely due to intracellular Cl-extracellular HCO-3- exchange. Recovery from an alkaline load was primarily mediated by anion exchange, and the dependence of maximal anion exchange rates on pH-i was very different in the absence and presence of HCO-3-. In its absence, maximal anion exchange (Cl--OH-) rates increased slowly over the tested pH-i range from 6.4 to 7.8. In the presence of HCO-3-, however, there was an S-shaped dependence of maximal flux rates on pH-i, with a steep increase in flux rates between 6.8 and 7.5. The data indicate that, in isolated rabbit parietal cells, Na+-H+ and Na+-independent Cl- -base exchangers are the principal regulators of pH-i and that a Na+-HCO-3- cotransporter is not involved. Both Na+-H+ and Cl--HCO-3- exchange rates appear to be strongly regulated by an internal proton-sensitive "modifier site."