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  • Title: [Characterization of proton pump and osmotic water transport in endocytic vesicles from rat kidney proximal tubule].
    Author: Shi LB, Ye RG, Lencer WI, Verkman AS.
    Journal: Sheng Li Xue Bao; 1990 Apr; 42(2):105-13. PubMed ID: 2142810.
    Abstract:
    The characteristics of ATP-driven proton and osmotic water transport were studied in endocytic vesicles isolated from rat kidney proximal tubule labelled in vivo with fluorescein isothiocyanate-dextran (FITC-dextran). ATP-driven proton transport was measured from the time course of endosome pH following addition of external ATP. The rate of endosome acidification and the minimum pH were dependent on the ATP concentration. At an initial endosome pH of 7.4, the final pH values were 7.30, 6.99, 6.68, 6.38 and 6.39 at [ATP] = 0.005, 0.05, 0.5, 5 and 10 mmol/L, respectively. The acidification was inhibited by 97% at 0.5 mmol/L N-ethylmaleimide but was not affected by vanadate and oligomycin. Osmotic water permeability was determined in the same endosomes from the rapid kinetics of FITC-dextran fluorescence following an inward sucrose gradient. The osmotic water permeability coefficient was 0.03 cm/s at 23 degrees C. Water permeability was inhibited by 70% with addition of 0.5 mmol/L mercuric chloride. The inhibition was reversed completely by adding 5 mmol/L mercaptoethanol. These data demonstrate that proximal tubule endosomes contain a proton ATPase and water channel. The endocytic process may be important for regulation of acidification and fluid resorption in the proximal tubule.
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