Intracellular localization of alkaline phosphatase in freshly isolated foetal rat hepatocytes.

The cytochemical localization of alkaline phosphatase activity in foetal rat hepatocytes was examined in relation to the pattern of cell to cell attachment during cell isolation and culture. In foetal hepatocytes in vivo, alkaline phosphatase was exclusively localized on the bile canalicular membrane. In freshly isolated foetal hepatocytes, however, the activity was present in the endoplasmic reticulum, nuclear envelope, Golgi apparatus, tubulo-vesicular organelles, and over the entire plasma membrane. In monolayer cells cultured for one or two days, the activity was localized on the reconstituted bile canalicular membrane, plasma membrane sites adjacent to neighbouring cells and on the bottom surface of the monolayer, but was detected in none of the intracellular organelles. Biochemical alkaline phosphatase activity did not change during isolation of the cells. These results suggest that, in foetal hepatocytes, loss of cell-cell contact may induce a temporal disturbance, or dedifferentiation, in their membrane system.