A domain-specific marker for the hepatocyte plasma membrane. II. Ultrastructural localization of leucine aminopeptidase to the bile canalicular domain of isolated rat liver plasma membranes.

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Abstract
Leucine aminopeptidase (LAP) is an integral membrane glycoprotein localized to the apical membrane domain of intestinal and kidney epithelial cells. By indirect immunofluorescence, antibodies raised against rat intestinal LAP recognized a similar protein concentrated in the bile canalicular (BC) domain of the hepatocyte in situ. This localization was extended to the ultrastructural level. When a saponin-permeabilized, agarose-embedded plasma membrane (PM) fraction was incubated with affinity-purified anti-LAP, 85% of the protein A-gold particles associated with the 3 recognizable PM domains were present in the BC. The levels of labeling on the other 2 domains (sinusoidal and lateral) did not exceed that observed with nonimmune controls. The concentration of LAP in the BC domain in isolated PM sheets prompted us to use this antigen for the affinity isolation of BC membrane.

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