Internalization of EGF and transferrin measured as the rate of uptake of 125l‐labeled ligands was compared in the cell line CCL39 and a mutant derivative, PS120, lacking the Na+/H+ antiport system. No significant alteration was detected between the two cell lines. In contrast, pretreatment of the mutant cells PS‐120 with 20 mM NH4Cl for 30 min to decrease persistently intracellular pH resulted in an increase in 125I‐EGF and 125I‐transferrin uptake by 60% and 25%, respectively. However, similar NH4Cl pretreatment of the parental cell line, CCL‐39, which only affected intracellular pH very transiently did not cause an increase of ligand uptake. The binding of 125I‐EGF to CCL‐39 and PS‐120 cells with or without NH4Cl pretreatment showed that NH4Cl pretreatment did not affect EGF binding in either CCL‐39 or PS‐120 cells. Since cells regulate intracellular pH by ion transport systems, we also examined the role of Na+, K+‐ATPase. Ouabain, an inhibitor of Na+, K+‐ATPases, showed no effect on 125I‐EGF uptake in either of the cell types with or without NH4Cl pretreatment. Taken together, these results suggest that the plasma membrane‐bound Na+/H+ antiport, a major pHi‐regulating system in vertebrates, indirectly plays a role in ligand internalization through regulation of intracellular pH.
ASJC Scopus subject areas
- 醫藥 (全部)