AJP - Gastrointestinal and Liver Physiology, Vol 254, Issue 5 732-G740, Copyright © 1988 by American Physiological Society
Stimulation of taurocholate and glycocholate efflux from the rat hepatocyte by arginine vasopressin
W. F. Kuhn and D. A. Gewirtz
Department of Medicine, Medical College of Virginia, Richmond 23298.
Vasopressin induces alterations in the transmembrane distribution of the
bile salts taurocholate and glycocholate but not of cholate,
chenodeoxycholate, or chenodeoxycholate derivatives in isolated rat
hepatocytes in suspension. Studies were conducted to define the specific
transport events modulated by vasopressin. Unidirectional uptake of
cholate, taurocholate, and glycocholate, monitored within a 15-s time
frame, is not altered by vasopressin. Km values for cholate, taurocholate,
and glycocholate influx were found to be 57, 12, and 26 microM,
respectively. Vmax values for influx of cholate, taurocholate, and
glycocholate were 1.7, 1.8, and 2.4 nmol.mg protein-1.min-1, respectively.
At half-maximal effective concentrations, arginine vasopressin increases
unidirectional efflux of taurocholate by 34% (EC50 = 1.5 X 10(-9) M) and
glycocholate by 17% (EC50 = 5 X 10(-9) M). In the presence of 0.05 microM
arginine vasopressin, the apparent Km value for taurocholate efflux
decreases from 1.57 mM (control) to 0.94 mM; for glycocholate, the apparent
Km decreases from 5.19 mM (control) to 3.22 mM. Vasopressin does not
significantly change the Vmax values for taurocholate and glycocholate
efflux (0.40 and 1.05 nmol.mg protein-1.min-1, respectively). These studies
suggest that modulation of bile salt efflux by vasopressin may be utilized
to probe bile salt transport pathways in the rat hepatocyte.
