title: Selective modification of the kinetic properties of Na+/H+ exchanger by cell shrinkage and swelling.
abstract: The effect of volume perturbation on the interaction of Na+ and H+ with the intracellular and extracellular faces of the Na+/H+ exchanger was studied in UMR-106 cells, a rat osteosarcoma cell line. Osmotic shrinkage of the cells stimulated the activity of the Na+/H+ exchanger. Kinetic analysis of this stimulation demonstrated that in hyperosmotically stressed cells, the apparent affinities for intracellular H+ and intracellular Na+ are modified in opposite directions. While there is an increased apparent affinity for protons from 0.275 +/- 0.03 to 0.107 +/- 0.025 microM in isotonic and hypertonic conditions, respectively, the apparent affinity for intracellular Na+ decreases from 83 +/- 9 to 126 +/- 6 mM under the same conditions. Osmotic swelling induced a decreased exchanger activity which appeared to involve reduction in Vmax only without changes in the apparent affinities of either H+i or Na+i. We conclude that: 1) osmotic shrinkage and swelling modify the kinetic behavior of the Na+/H+ exchanger in different modes; 2) in hyperosmotically stressed cells, the interactions of intracellular H+ and Na+ are modified in a selective mode. The described phenomenon may serve as a general mechanism for activation of the exchanger by various stimuli.
authors.affiliation: Laboratory of Membrane Biology, Veterans Administration Medical Center, Los Angeles, California.
authors.forename: J
authors.initials: J
authors.lastname: Green
authors.forename: D T
authors.initials: DT
authors.lastname: Yamaguchi
authors.forename: C R
authors.initials: CR
authors.lastname: Kleeman
authors.forename: S
authors.initials: S
authors.lastname: Muallem
mesh_terms: D000818:Animals; D001826:Body Fluids / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D006863:Hydrogen-Ion Concentration; D007424:Intracellular Fluid / Q000502:physiology*; D007700:Kinetics; D009995:Osmosis; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers
chemical_list: D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D012964:Sodium