Role of Na+/H+ antiport in intracellular pH regulation by rabbit enterocytes

The steady-state intracellular pH (pHi) of isolated rabbit enterocytes was determined using 9-aminoacridine, a fluorescent weak base, and the null-point method with digitonin. When cells are incubated in a Na+-containing solution, the estimated value of pHi was in the range of 7.10-7.20, whereas it was 6.60-6.70 when cells were incubated in a Na+-free solution, indicating an important role of external Na+ in maintaining pHi at a slightly alkaline level. Pulse injection of Na+ into a Na+-free cell suspension induced a slowly developing alkalinization of pHi. The time course of the alkalinization was found to be dependent on the Na+ concentration. Li+ had the same effect as Na+, while K+ had a slight effect. Amiloride inhibited the effects of Na+ dose-dependently. These results indicate that the Na+/H+ antiport plays an important role in maintaining the pHi at a neutral or slightly alkaline level in the intact enterocytes.