AJP - Gastrointestinal and Liver Physiology, Vol 254, Issue 5 761-G767, Copyright © 1988 by American Physiological Society
Selective modulation of hepatic and ileal Na+-K+-ATPase by bile salts in the rat
F. R. Simon, E. Sutherland and J. Sutherland
University of Colorado School of Medicine, Division of Gastroenterology, Denver.
Sodium-potassium adenosinetriphosphatase (Na+-K+-ATPase) is modulated by
functional demands. We determine whether Na+-K+-ATPase specific activity
was changed by oral administration of different bile salts and whether
upregulation in the liver is due to increased numbers of catalytic units.
In rats after bile duct drainage for 18 h, Na+-K+-ATPase activity was
reduced to 50% of control in liver and ileum but unchanged in jejunum and
kidney. Increased Na+-K+-ATPase activity after short-term feeding of bile
salts was noted only following trihydroxy bile salts, i.e., taurocholate
(100 mg/100 g body wt) increased hepatic Na+-K+-ATPase 143% and ileum 138%
above control, whereas jejunum and kidney were unchanged. Chronic feeding
of trihydroxy bile salts for 4 days increased hepatic Na+-K+-ATPase
(214-260%) and alkaline phosphatase (189-274%), whereas 5'-nucleotidase and
Mg2+-ATPase activities were unchanged from control. Plasma membrane
Na+-K+-ATPase activity significantly increased as early as 4 h after
taurocholate administration, whereas homogenate activity did not rise until
16 h; both reached a new steady state between 24 and 48 h. Sixteen hours
after bile salt feeding, increased Na+-K+-ATPase activity was blocked by
cycloheximide, and in the liver increased enzyme activity (179%) was
associated with a comparable change in sodium-dependent [gamma-32P]ATP
binding (162%) to liver plasma membrane fractions. These studies show
Na+-K+-ATPase activity adapts selectively in liver and ileum following
administration of trihydroxy bile salts, and the process involves increased
density of Na+-K+ pump sites on the liver plasma membrane.
