Amiloride transport in rabbit renal brush-border membrane vesicles.
Rabbit renal brush-border membrane vesicles (BBMV) were used to study amiloride transport across the luminal membrane of proximal tubular cells. An outwardly directed H+ gradient (pHi 6.0; pHo 7.5) stimulated 8 microM [14C]-amiloride uptake into BBMV and supported a transient "active" accumulation of substrate consistent with the presence of an amiloride-H+ exchange process. Uptake was inhibited, in the presence or absence of a pH gradient, by 1 mM unlabeled amiloride or 20 mM tetraethylammonium (TEA). Amiloride transport was not directly affected by the presence of 100 mM Na+ in the extravesicular medium, suggesting that Na-H exchange did not mediate amiloride flux. Amiloride transport was a saturable process with a maximal flux (under pH gradient conditions) of 3 nmol.mg-1.min-1 and an apparent Kt of 8 microM. TEA acted as a competitive inhibitor of this process with an apparent Ki of approximately 80 microM, similar to the Kt of TEA transport via the TEA-H+ exchanger. Likewise, amiloride acted as a competitive inhibitor of TEA uptake with an apparent Ki of approximately 11 microM. Preloading BBMV with 1-2 mM TEA stimulated the rate of amiloride uptake and supported a transient active accumulation of amiloride. We conclude that amiloride and TEA are transported by a common pathway in BBMV, which involves a carrier-mediated exchange with H+ and which may play a role in the tubular secretion of these compounds.
Wright
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Department of Physiology, College of Medicine, University of Arizona, Tucson 85724.
Wunz
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TM
D000584:Amiloride / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002250:Carbon Radioisotopes; D006863:Hydrogen-Ion Concentration; D007672:Kidney Cortex / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D007700:Kinetics; D008871:Microvilli / Q000378:metabolism*; D011817:Rabbits; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000378:metabolism / Q000494:pharmacology
D002250:Carbon Radioisotopes; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D000584:Amiloride