title: The role of intracellular pH in ligand internalization.
abstract: Internalization of EGF and transferrin measured as the rate of uptake of 125I-labeled ligands was compared in the cell line CCL39 and a mutant derivative, PS-120, 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.
mesh_terms: D000643:Ammonium Chloride / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001826:Body Fluids / Q000378:metabolism*; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004815:Epidermal Growth Factor / Q000378:metabolism*; D066246:ErbB Receptors; D005347:Fibroblasts / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007424:Intracellular Fluid / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000032:analysis / Q000187:drug effects; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D014168:Transferrin / Q000378:metabolism*
chemical_list: D007473:Ion Channels; D011956:Receptors, Cell Surface; D014168:Transferrin; D000643:Ammonium Chloride; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D000254:Sodium-Potassium-Exchanging ATPase