AJP - Gastrointestinal and Liver Physiology, Vol 253, Issue 2 232-G240, Copyright © 1987 by American Physiological Society
Uncoupling of the secretory pathways for IgA and secretory component by cholestasis
T. M. Kloppel, T. C. Hoops, D. Gaskin and M. Le
Circulating polymeric immunoglobulin A (IgA) binds to secretory component
(SC) on the surface of rat hepatocytes and is internalized and transported
by vesicles to the canalicular membrane where the IgA-SC complex is
secreted into bile. To further characterize this transport pathway, we
examined the effects of bile flow reduction or transient bile duct
obstruction on the secretion of IgA and SC into bile. In response to
gradually increasing resistance to bile flow, the biliary concentration of
IgA decreased as bile flow decreased, whereas total biliary protein
concentration was little changed. After 2 h of bile duct clamping, the
amount of IgA secreted into bile during the postclamp period was decreased
to one-tenth of control values. Similarly, transport of biosynthetically
labeled monoclonal IgA ([3H]MoIgA) during the postclamp period was reduced
three-fold. In contrast to the impairment in IgA secretion, secretion of SC
continued at nearly normal levels after resumption of bile flow. The
reduced transport of IgA was not due to a failure of IgA to reach the
hepatocyte, a functional alteration of the IgA, or a decrease in the number
of hepatic IgA receptors. Our studies indicate that secretion of IgA is
sensitive to bile flow and that the biliary secretory pathways for IgA and
SC are dissociated after brief periods of cholestasis.
