title: Na(+)-H+ exchange, but not Na(+)-K(+)-ATPase, is present in endosome-enriched microsomes from rabbit renal cortex.
abstract: Previous studies have demonstrated a Na(+)-dependent decrease in the ATP-generated acidification of endosomes and have attributed it to the presence of either a Na(+)-H+ exchanger or a Na(+)-K(+)-adenosinetriphosphatase (ATPase) in parallel with the vacuolar H(+)-ATPase. In the present study we have examined the possibility that both of these two Na+ transporters might be present in endosome-enriched microsomes isolated from rabbit renal cortex. After the establishment of a stable pH gradient by ATP in this preparation, addition of Na+ induced a decrease in the pH gradient. Expression of this effect of Na+ did not require the presence of ATP or K+. Choline and K+ had no effect on the ATP-dependent pH gradient, but addition of Li+ caused a small reduction in the pH gradient. Amiloride, ouabain, and vanadate had no effect on the Na(+)-induced dissipation of the ATP-driven pH gradient. In addition, a pH gradient-dependent 22Na+ uptake by the endosomal vesicles that was insensitive to amiloride, ouabain, or vanadate was demonstrated. These results provide evidence against the presence of a Na(+)-K(+)-ATPase in endosome-enriched microsomes from the renal cortex and support the existence of an amiloride-insensitive Na(+)-H+ exchanger in parallel with the vacuolar H(+)-ATPase. This endosomal Na(+)-H+ exchanger might have important implications for the regulation of vacuolar H(+)-ATPase activity as well as proximal tubule acidification.
authors.affiliation: Department of Medicine, Tufts University School of Medicine, Boston, Massachusetts.
authors.forename: S A
authors.initials: SA
authors.lastname: Hilden
authors.forename: K B
authors.initials: KB
authors.lastname: Ghoshroy
authors.forename: N E
authors.initials: NE
authors.lastname: Madias
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007672:Kidney Cortex / Q000378:metabolism* / Q000648:ultrastructure; D008861:Microsomes / Q000378:metabolism*; D015388:Organelles / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits; D012964:Sodium / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014638:Vanadates / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D014638:Vanadates; D010042:Ouabain; D000584:Amiloride; D000255:Adenosine Triphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium