PLASMA MEMBRANES OF THE RAT LIVER Isolation and Enzymatic Characterization of a Fraction Rich in Bile Canaliculi

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 0/, 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 .