In vitro effect of free bile acids on the bile canaliular membrane phospholipids in the rat

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Abstract
Liver cell plasma membranes of male rats were isolated and separated into 2 fractions, one rich in bile canalicular membranes (BCM) and the other comprising the rest of the plasma membranes (PM). Aliquots of BCM, PM and microsomes were incubated with deoxycholic, chenodeoxycholic or cholic acid at bile acid-membrane phospholipid mole ratios up to 100, and the phospholipids solubilized from the membranes were analyzed. Phospholipid solubilization from the PM and from microsomes was linear and apparently nonselective, while that from the BCM was biphasic and distinctly selective. Phosphatidyl choline and phosphatidyl ethanolamine made up 90% of the phospholipids solubilized from the BCM at a bile acid-membrane phospholipid mole ratio sufficient to solubilize about 50% of the total phospholipids of the BCM. Of particular interest was the observation that the molecular species and fatty acid composition of the phospholipids solubilized from the BCM under these experimental conditions were similar to those of bile obtained from the same animal, and were quite unlike those solubilized at higher bile acid- phospholipid mole ratios. The data are discussed in terms of the mechanism of the biliary secretion of phospholipids.