Characterization of the Na+/H+ exchanger in human epidermoid carcinoma A431 vesicles.
A previous report from this laboratory (Rothenberg et al., 1983a) demonstrated the presence of an Na+/H+ exchanger in human epidermoid carcinoma A431 cells. We now characterize surface-derived membrane vesicles from this cell line which contain a functional Na+/H+ exchanger. The Na+/H+ exchanger in A431 vesicles shares a number of characteristics in common with previously described Na+/H+ exchangers including the following: (1) Na+ uptake is stimulated by an outward-directed pH gradient and inhibited by an inward-directed pH gradient. (2) Na+ uptake is inhibited by amiloride and its analogs and their relative effectiveness is similar in vesicles and A431 cells. (3) The Na+/H+ exchanger uses Na+ or Li+ as a substrate but not K+ or Cs+. (4) H+ efflux is stimulated by an inward-directed Na+ gradient and inhibited by the amiloride analog 5-N-dimethylamiloride. The Na+/H+ exchanger in these membrane vesicles is activated allosterically by low intravesicular pH. The apparent pKa of the activating site is 6.4-6.6, characteristic of the NA+/H+ exchanger before activation by mitogens.
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D002294:Carcinoma, Squamous Cell / Q000378:metabolism* / Q000473:pathology; D002412:Cations / Q000494:pharmacology; D002478:Cells, Cultured; D006801:Humans; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007474:Ion Exchange; D012964:Sodium / Q000378:metabolism*
D002412:Cations; D000584:Amiloride; D006859:Hydrogen; D012964:Sodium