Regulation of taurocholate and ursodeoxycholate uptake in hamster
hepatocytes by calcium-mobilizing agents.
Bouscarel, Bernard, Syed Reza, Laura A. Dougherty, Hans Fromm, and
Robert Nussbaum.
Division of Gastroenterology and Nutrition, Department of Medicine,
The George Washington University Medical Center, Washington, DC
20037
APStracts 3:0134G, 1996.
In isolated hamster hepatocytes, the Ca2+ ionophore A23187 immediately
decreased the uptake rate of taurocholic acid (TCA) by 60-70%, while
it slowly inhibited that of ursodeoxycholic acid (UDCA) by a maximum
of 35-45%, with a respective inhibition constant (Ki) of 0.36 [mu]M
and 1.93 [mu]M. In contrast to ionomycin, which mimicked the effect
of A23187, vasopressin inhibited the bile acid uptake rate by 40% and
45%, respectively, only after 5 to 10 min preincubation. The Na+
-dependent bile acid transport was exclusively inhibited by these
agents, and this inhibition was independent of extracellular Ca2+.
However, intracellular Ca2+ depletion with EGTA or chelation with
BAPTA resulted in 40-50% inhibition of the uptake rate of both bile
acids. The exogenous protein kinase C activator, phorbol 12-myristate
13-acetate (PMA) but not the non-active 4[alpha]-phorbol,
significantly inhibited TCA uptake rate. While both A23187 and
ionomycin immediately increased and decreased the cellular Na+ and K+
concentration, respectively, neither vasopressin nor PMA had a
significant effect on the cellular concentration of these cations,
even after 10 min incubation. Furthermore, the effect of A23187 and
ionomycin on TCA uptake and Na+ flux, respectively, disappeared after
40 min preincubation, and further addition of the ionophore remained
without effect. However, after 40 min incubation with A23187, PMA was
still able to inhibit TCA uptake. Therefore, A23187 and ionomycin
transiently inhibited Na+-dependent uptake of both TCA and UDCA, in
part, due to transient alteration of the cellular Na+ and K+
concentration. Vasopressin and PMA inhibited Na+-dependent bile acid
uptake, at least in part, through protein kinase C activation.
Received 28 February 1995; accepted in final form 28 June 1996.
APS Manuscript Number G86-5.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996