Cytosolic pH sensitivity of an expressed human NHE-1 Na(+)-H+ exchanger.

Academic Article

Abstract

  • These studies examined the effects of protein kinase C activation and calmodulin inhibition on the amiloride-sensitive NHE-1 isoform of the Na(+)-H+ exchanger in defined host cells. Our objective was to define differences in the cellular regulatory responses using a specified isoform of the Na(+)-H+ exchanger. Suspended cells were loaded with 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF) and preacidified to a cytosolic pH of 6.2. Wild-type mouse Ltk- cells, human A-431 cells, and mutant mouse fibroblasts stably transfected with the human NHE-1 isoform (LAP+ cells) were examined to define the maximal rate of transport (Vmax) in response to 140 mM external Na+, the Hill stoichiometric coefficient, and the cytosolic pH at which the NHE-1 isoform was half-maximally stimulated (pH50). The mouse NHE-1 isoform had a greater affinity for cytosolic H+ than the human NHE-1 isoforms. Calmodulin antagonism with N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide reduced the Vmax and shifted the pH50 in the acidic direction, especially in the A-431 cells. Protein kinase C stimulation had a similar effect in A-431 cells and little effect in the wild-type (Ltk-) and transfected (LAP+) mouse cells. While the NHE-1 isoform contains several potential phosphorylation sites, the cellular milieu in which the isoform is expressed has an important effect on the modulation of NHE-1 activity.

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    Keywords

  • Amiloride, Animals, Calmodulin, Carrier Proteins, Cytosol, Genetic Vectors, Humans, Hydrogen-Ion Concentration, Kinetics, L Cells, Mice, Plasmids, Restriction Mapping, Sodium-Hydrogen Exchangers, Sulfonamides, Tetradecanoylphorbol Acetate, Transfection, Tumor Cells, Cultured

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    Author List

  • Takaichi K; Balkovetz DF; Van Meir E; Warnock DG

    • Start Page

  • C944

    • End Page

  • C950

    • Volume

  • 264

    • Issue

  • 4 Pt 1