ISSN:
1432-1424
Keywords:
proximal tubule
;
brush border
;
H+-ATPase
;
vacuolar
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary Exposure of porcine renal brush-border membrane vesicles to 1.2% cholate and subsequent detergent removal by dialysis reorients almost all N-ethylmaleimide (NEM)-sensitive ATPases from the vesicle inside to the outside. ATP addition to cholate-pretreated, but not to intact, vesicles causes H+ uptake as visualized by the ΔpH indicator, acridine organge. The reoriented H+-pump is electrogenic because permeant extravesicular anions or intravesicular K+ plus valinomycin enhance H+ transport. ATP stimulates H+ uptake with an apparentK m of 93 μm. Support of H+ uptake andP i liberation by ATP〉GTP≈ITP〉 UTP indicates a preference for ATP and utilization of other nucleotides at lower efficiency. ADP is a potent, competitive inhibitor of ATP-driven H+ uptake,(K i , 24 μm). Mg2+ and Mn2− support ATP-driven H+ uptake, but Ca2+, Ba2+ and Zn2+ do not. Imm Zn2+ inhibits MgATP-driven H+ transport completely. NEM-sensitiveP i liberation is stimulated by Mg2+ and Mg2− and, unlike H+ uptake, also by Ca2+ suggesting Ca2+-dependent ATP hydrolysis unrelated to H+ transport. The inside-out oriented H+-pump is relatively insensitive toward oligomycin, azide, N,N′-dicyclohexylcarbodiimide (DCCD) and vanadate, but efficiently inhibited by NEM (apparentK i , 0.77 μm), and 4-chloro-7-nitro-benzoxa-1,3-diazole (NBD-Cl; apparentK i , 0.39 μm). Taken together, the H+-ATPase of proximal tubular brush-border membranes exhibits characteristics very similar to those of “vacuolar type” (V-type) H+-ATPases. Hence,V-type H+-ATPases occur not only in intracellular organelles but also in specialized plasma membrane areas.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01868681
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