Effect of chronic hypokalemia on h + ,k + -atpase expression in rat
colon .
Codina, Juan, Thomas A. Pressley, and Thomas D. Dubose.
Departments of Internal Medicine, and Integrative Biology,
University of Texas-Houston Medical School, and Department of
Physiology, Texas Tech University Health Sciences Center
APStracts 3:0180F, 1996.
Although the kidney plays the major role in the regulation of systemic
K+ homeostasis, the colon also participates substantively in K+
balance. The colon is capable of both K+ absorption and secretion,
the magnitude of which can be modulated in response to dietary K+
intake. The H +,K +-ATPase has been proposed as a possible mediator
of K+ absorption in distal colon, but inhibitor profiles obtained in
recent studies suggest that two, and perhaps more, distinct H+,K+
-ATPase activities may be present in mammalian distal colon. We have
developed highly specific probes for the catalytic [alpha]-subunits
of colonic and gastric H+,K+-ATPase, [alpha]1-Na+,K+-ATPase and
[beta]-actin which were used in northern analysis of total RNA from
whole distal colon and stomach obtained from one of three
experimental groups of rats: 1) controls, 2) chronic dietary K+
depletion, and 3) chronic metabolic acidosis. The probe for the
colonic, but not the gastric H+,K+-ATPase [alpha]-isoform, hybridized
to distal colon total RNA in all groups. A significant increase in
colonic H+,K+-ATPase mRNA abundance was observed in response to
chronic dietary K+ depletion, but not to chronic metabolic acidosis.
The [alpha]1-isoform of Na+, K+-ATPase, which is also expressed in
distal colon, did not respond consistently to either chronic dietary
K+ depletion or chronic metabolic acidosis. The gastric probe did not
hybridize to total RNA from distal colon, but, as expected,
hybridized to total stomach RNA. However, the abundance of gastric
H+,K+-ATPase or Na+,K+-ATPase in stomach was not altered consistently
by either chronic dietary K+ depletion or metabolic acidosis. Under
the conditions of this study, it appears that the mRNA encoding the
colonic [alpha]-isoform is up-regulated by chronic dietary K+
restriction a condition shown previously to increase potassium
absorption in the distal colon.
Received 20 September 1995; accepted in final form 13 September
1996.
APS Manuscript Number F319-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996