Abstract
A method is described for the rapid isolation of a plasma membrane fraction containing a high concentration of intact bile canaliculi from the rat liver. Isolated bile canaliculi retain most of the ultrastructural features exhibited in the intact liver cell. The final fraction contains 5'-nucleotidase activity at approximately the same concentration as that in previous preparations of plasma membranes. In the presence of 0.01 M Mg(++), 5'-nucleotidase exhibits a double pH optimum at pH values of 7.5 and 9.5. The activities of glucose-6-phosphatase and alkaline phosphatase are present in low amounts. Cytochrome P-450 is not detectable. Na(+)-K(+)-activation of ATPase is observed to the extent of 20-36% in about half of the assays. The availability of a method for preparation of intact bile canaliculi should prove useful for studying the biochemical events associated with the transport of bile constituents into canaliculi.
Highlights
IntroductionPlasma membranes of adjoining parenchymal cells make up bile canaliculi (tubular structures with villous projections of membranes) which are readily identifiable by means of electron microscopy [15]
Plasma membranes of adjoining parenchymal cells make up bile canaliculi which are readily identifiable by means of electron microscopy [15]
We describe in this paper a rapid method for preparing a plasma membrane fraction from rat liver which contains relatively intact bile canaliculi in a good yield
Summary
Plasma membranes of adjoining parenchymal cells make up bile canaliculi (tubular structures with villous projections of membranes) which are readily identifiable by means of electron microscopy [15]. Bile canaliculi are the most proximal intrahepatic loci where various biliary constituents are transported from the parenchymal cells into the bile. Isolation of bile canaliculi would offer an excellent means of studying biochemical aspects of the transport phenomena associated with bile formation. We describe in this paper a rapid method for preparing a plasma membrane fraction from rat liver which contains relatively intact bile canaliculi in a good yield. Certain enzymatic properties of the isolated fraction have been studied and compared with those of the whole homogenate and microsomal fraction of the rat liver
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