Cholic Acid Binding to Isolated Rat Liver Plasma Membranes

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Abstract
Cholic acid binding to isolated rat liver plasma membranes was studied using a centrifugal filtration technique which allowed independent determination of free and membrane-bound cholic acid. Binding of cholic acid was very rapid and reversible. Scatchard analysis revealed at least 3 binding sites with high, medium and low affinity. The high affinity binding displayed saturability and isotope replacement, was not present in rat liver mitochondria and red blood cell ghosts, and was temperature dependent. This binding has a very low capacity with a dissociation constant in the physiological range of plasma cholic acid concentration and had an affinity for other common bile acids. Cholic acid binding to the high affinity binding site was not inhibited by estrone, .beta.-estradiol or cholesterol. The high affinity binding site may represent a specific binding site for cholic acid and may be specific for other common bile acids. This binding was not dependent on Na+ and was inhibited by bromosulfophthalein. Cholic acid binding to the high affinity site has some features in common with cholic acid uptake by isolated rat hepatocytes, and the high affinity binding site could be the postulated carrier for hepatic uptake of cholic acid.

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