H+,k+-atpase mediates net acid secretion in the rat terminal inner
medullary collecting duct.
Wall, Susan M., Alice V. Truong, and Thomas D. Dubose, Jr.
Division of Renal Diseases and Hypertension, University of Texas
Medical School, Houston, Houston, TX. 77030
APStracts 3:0141F, 1996.
Studies in our laboratory have demonstrated total CO2 absorption and
total ammonia secretion in the terminal inner medullary collecting
duct (tIMCD) perfused in vitro. The purpose of the present study was
to determine if the H+,K+-ATPase participates in proton secretion or
total CO2 absorption, JtCO2, in this segment. Tubules from the middle
third of the tIMCD were dissected from rats with chronic metabolic
acidosis (300 mM NH4Cl, 3-4 days in drinking water) and perfused in
vitro. Perfusate and bath were symmetrical solutions containing 5 mM
KCl, 6 mM NH4Cl and 25 mM NaHCO3. Bafilomycin A1 (5nM), a specific
inhibitor of the H+-ATPase, did not affect JtCO2 compared with
baseline (JtCO2, 3.0 + 1.0 and 3.0 + 0.8, n=6, P = NS), or with time
controls (n=4). With removal of luminal K+, JtCO2 fell from 2.8 + 0.6
to 1.6 + 0.4 pmol/mm/min (n=5, P < 0.05). To evaluate K+
-sensitive JtCO2 further, the effect of H+,K+-ATPase inhibition on
JtCO2 was explored using the specific H+,K+-ATPase inhibitor, Sch
28080. Addition of 10 [mu]M Sch 28080 to the luminal perfusate
decreased total CO2 absorption (JtCO2, 2.7 + 0.4 to 1.4 + 0.5
pmol/mm/min, n=5, P < 0.05), but did not alter transepithelial
membrane potential. Thus, luminal Sch 28080 addition, as well as
luminal K+ removal, limits apical H+ exit or OH-/HCO3- entry. These
results demonstrate that net acid secretion is mediated by the H+,K+
-ATPase in the tIMCD.
Received 4 January 1996; accepted in final form 30 July 1996.
APS Manuscript Number F2-6.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 29 August 1996