Transcellular transport of fluorescein in hepatocyte monolayers: evidence for functional polarity of cells in culture.

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Abstract
The rat liver in vivo transfers bile salts, proteins, and dyes from blood into bile. It is the purpose of this communication to demonstrate the maintenance of this transcellular transport in cultured adult rat hepatocytes. Two minutes after adding fluorescein (20 microgram/ml) to the culture medium, maximal cellular fluorescence was observed through the fluorescence microscope. Subsequently, intercellular clefts showed a steadily increasing fluorescence with a maximum between 5 and 20 min, resulting in a brightly fluorescent network of intercellular gaps. The following observations are taken as evidence that these findings reflect cellular uptake and canalicular secretion of the dye. First, the same sequence of observations was made upon addition of fluorescein diacetate (a nonfluorescent precursor of fluorescein), proving that the compound had been taken up and metabolized in the cells to fluorescein before secretion into intercellular clefts. Second, preincubation of the monolayers with the cholestatic bile salt taurolithocholate (100 mumol/liter) suppressed almost completely intercellular but not cellular fluorescence. It is concluded that hepatocytes in culture show a functional polarity permitting the transcellular transport of substances bound for biliary secretion.