Dietary k+ restriction upregulates total and sch 28080- sensitive
bicarbonate absorption in rat timcd.
Wall, Susan M., Pramod Mehta, and Thomas D. Dubose, Jr., University Of
Texas, Medical School At Houston, Houston, Tx. .
Susan M. Wall, M.D., Division of Renal Diseases and Hypertension,
University of Texas, Medical School at Houston, 6431 Fannin, M.S.B.
4.148, Houston, TX. 77030, Phone: (713) 500-6868, FAX: (713) 500
-6882, e-mail: swall@heart.med.uth.tmc.edu
APStracts 5:0126F, 1998.
In tIMCD tubules from rats with chronic metabolic acidosis, our
laboratory has shown that bicarbonate absorption, (JtCO2), is
inhibited by removal of K+ from the luminal fluid or by the addition
of Sch 28080 to the perfusate. The present study asked if total
and/or Sch 28080-sensitive JtCO2 is regulated by changes in systemic
K+ homeostasis. Rat tIMCD tubules were perfused in vitro in
symmetric, HCO3-/CO2-buffered solutions containing 10 mM KCl, 6 mM
NH4Cl. Total and Sch 28080-sensitive JtCO2 were measured in rats with
varying K+ intake. In K+-replete rats, baseline JtCO2 was 2.1 + 0.3
pmol/mm/min (n=6). In rats fed a K+-deficient diet for 3 days JtCO2
was 5.4 + 0.7 pmol/mm/min (n=16, P<0.05). To determine the
mechanism for the increase in HCO3- absorption observed with K+
restriction, the Sch 28080-sensitive component of JtCO2 was measured
in each treatment group. Following the addition of Sch 28080 (10
[mu]M) to the perfusate, a 40% reduction in JtCO2 was observed in K+
restricted rats. JtCO2 was not reduced following the addition of Sch
28080 in rats with normal K+ intake. Because Sch 28080-sensitive
JtCO2 was increased in K+ restricted rats, Sch 28080-sensitive JtCO2
was studied further in tIMCD tubules from rats in this treatment
group. In K+ restricted rats, JtCO2 decreased by 20% following the
addition of 5 mM ouabain to the perfusate. This ouabain-induced
decline in JtCO2 was observed both in the presence and in the absence
of Sch 28080. We conclude that total and Sch 28080-sensitive net acid
secretion is increased with dietary K+ restriction. However, since
40-50% of JtCO2 is both Sch 28080-and ouabain-insensitive, future
studies will be necessary to define other mechanisms of luminal
acidification in the rat tIMCD.
Received 17 February 1998; accepted in final form 16 July 1998.
APS Manuscript Number F34-8.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 21 September 1998