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We examined the changes in localization of alkaline phosphatase (ALP) and mannosidase II (man II), a Golgi marker, after colchicine treatment of primary cultures of fetal rat hepatocytes, using double immunofluorescence staining and confocal laser microscopy. In hepatocytes cultured in basal medium, ALP was localized in the perinuclear cytoplasm, and man II was observed in the Golgi region of the cytoplasm. When hepatocytes were cultured in dexamethasone-supplemented medium, ALP was also localized in the plasma membrane surrounding the bile canaliculus-like structure that was formed between adjacent cells. In hepatocytes cultured in the same medium containing colchicine, the structure of microtubules in the cytoplasm was lost, man II exhibited granular distribution scattering throughout the cytoplasm, and ALP was localized in coarse granular sites of the cytoplasm. However, ALP was not colocalized at the same sites as man II. The present study indicated that colchicine inhibits the dexamethasone-promoted translocation of ALP to the plasma membrane surrounding the bile canaliculus-like structure in primary cultures of fetal rat hepatocytes by disassembling microtubules and discomposing the Golgi complex.

The localization of alkaline phosphatase (ALP) and four proteins related to intercellular junctions in primary cultures of fetal rat hepatocytes was immunocytochemically investigated using fluorescence-labeled antibodies and confocal laser microscopy in order to determine whether the formation of intercellular junctions at the borders between adjacent rat hepatocytes becomes the trigger of translocation of ALP from the cytoplasm to the plasma membrane. Dexamethasone (DEX) which was supplemented in the base medium promoted the translocation of ALP from the cytoplasm to the plasma membrane surrounding bile canaliculus-like intercellular spaces and the appearance of connexin-32 at cell borders between adjacent fetal hepatocytes. E-cadherin, occludin and ZO-1 were localized at the cell borders between adjacent fetal hepatocytes irrespective of the presence of DEX. Occludin and ZO-1 were further localized along the plasma membrane surrounding bile canaliculus-like intercellular spaces formed by DEX. The present study indicates that the formation of adherens and tight junctions between adjacent rat hepatocytes does not become the trigger of ALP translocation from the cytoplasm to the plasma membrane, although we cannot be certain of whether the formation of gap junctions between adjacent rat hepatocytes triggers ALP translocation.

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