LOCALIZATION OF GAMMA-GLUTAMYL-TRANSPEPTIDASE AND ALKALINE-PHOSPHATASE IN PRIMARY CULTURES OF FETAL-RAT HEPATOCYTES

The localization of gamma-glutamyltranspeptidase (GGT) and alkaline ph osphatase (ALP) in primary cultures of fetal rat hepatocytes was inves tigated using enzyme cytochemical and immunocytochemical techniques. W hen hepatocytes were cultured in a medium supplemented with dexamethas one (DEX) or dimethylsulfoxide (DMSO), both enzymes were observed in t he plasma membranes along the intercellular spaces that developed betw een adjacent hepatocytes. On the other hand, in hepatocytes cultured i n the basic medium or in medium supplemented with transforming growth factor-beta (TGF-beta), the enzymes were found in the limited area of the cytoplasm surrounding the nuclei. Connexin-32, a subunit of protei ns that comprise gap junctions, was detected along the cell borders in hepatocytes cultured in DEX or DMSO-supplemented medium, but was not found in hepatocytes cultured in the basic medium or in medium supplem ented with TGF-beta. However, the DEX and DMSO supplements did not cau se any changes in the distribution of microtubules in hepatocytes, and numerous microtubular fibers were observed to extend in a radial patt ern from the nuclei to the periphery of the cytoplasm in all hepatocyt es, irrespective of medium type. These results indicate that assessmen t of the location of GGT and ALP may help determine the level of hepat ocyte differentiation in cultured rat hepatocytes and that intracellul ar factors other than microtubules are involved in the transport of th ese enzymes from the cytoplasm to the plasma membrane.