Cytosolic pH regulation in chicken enterocytes: Na(+)-independent regulatory cell alkalinization

The mechanisms involved in intracellular pH (pHi) recovery from an acid load have been investigated in enterocytes isolated from chicken. Following an intracellular acidification, by abrupt withdrawal of NH4Cl, pHi alkalinized in the nominally absence of Na+ and bicarbonate. This Na(+)- and bicarbonate-independent (NBI) regulatory cell alkalinization became negligible when the pHi has reached a value of approx. 6.85. Addition of Na+ induced a rapid pHi recovery to control values. Rotenone, DCCD, vanadate, NBD-Cl, SCH 28080 and EIPA inhibited the NBI cell alkalinization, whereas bafilomycin A1, ouabain and H2-DIDS were without effect. Na(+)-dependent pHi recovery from an acid load was inhibited by EIPA and unaffected by SCH 28080 or DCCD. The rate of NBI cell alkalinization was a linear function of the electrochemical proton gradient. In high external K+ buffer plus valinomycin the line goes through the origin. Gramicidin accelerated the rate of NBI cell alkalinization, whereas it was slightly reduced by low external potassium. The results demonstrate that in intestinal epithelial cells exist at least two mechanisms for proton secretion: a Na(+)-H+ exchanger and a Na(+)- and bicarbonate-independent proton transport system. This latter mechanism appears to be a proton conductance pathway.