Rates of Synthesis and Selective Loss into the Bile of Four Rat Liver Proteins and the Polymeric IgA Receptor

Abstract

Hepatocytes have three distinct plasma membrane (PM) surfaces: apical (bile canaliculus), basal (blood) and lateral. Each domain contains distinct membrane proteins, such as the apical proteins, dipeptidyl peptidase IV (DPPIV) and HA4 (Ecto-ATPase) (Hubbard et al., 1985, Bartles et al., 1985), a basolateral protein, CE9, (Hubbard et al., 1985) and a basolateral protein which is concentrated on the lateral surface, HA321 (Braiterman and Hubbard, 1985). We have determined the half-lives and cellular amounts of these four PM molecules, their rates of synthesis and the amount of loss from the cell that can be accounted for by their release into bile. We have compared these values to those for the pIgA-receptor (pIgA-R), a sacrificial receptor, which travels first to the basolateral surface where it can bind pIgA, is then transported to the apical surface, and is subsequently cleaved externally and released into the bile as secretory component (SC) (Brown and Koppel, 1989).