Amino Acid Transport In Liver
Published 1992 · Chemistry
The liver is recognized to play an important role in controlling the levels of free amino acids in the plasma, through both import and export of individual amino acids into or out of the hepatocyte (Schimassek and Gerok 1965, Ishikawa 1975). Much effort has been devoted to elaborate the mechanisms and regulatory properties of amino acid transport in liver and its relevance for overall liver cell function. Regarding amino transport in liver, two phenomena deserve special attention. First, hepatocytes in situ are polar cells exhibiting differences in amino acid transport properties across the basolateral (sinusoidal) and the canalicular membrane. Second, despite similar appearance under the light-microscope, hepatocytes are functionally different and there is marked hepatocyte heterogeneity in amino acid transport across the sinusoidal membrane. This must be kept in mind when transport studies with isolated hepatic plasma membrane vesicles or isolated hepatocytes are considered. In these experimental systems the cellular polarity is lost and cell heterogeneity regarding transport is frequently lost. Several approaches have been used to overcome these problems. They include preparations of plasma membrane vesicles from the sinusoidal and canalicular domains of the cell membrane, attempts to isolate hepatocytes from the periportal or perivenous areas of the acinus, the use of histoautoradiography and the use of radiolabel incorporation studies in the intact perfused liver by following the metabolic fate of an amino acid taken up into pathways which are characteristic for certain hepatocyte subpopulations.