Biliary excretion in primary rat hepatocytes cultured in a collagen-sandwich configuration.

The objective of the present investigation was to examine the functional reestablishment of polarity in freshly isolated hepatocytes cultured between 2 layers of gelled collagen (sandwich configuration). Immunoblot analysis demonstrated that the canalicular multispecific organic anion transport protein (multidrug resistance-associated protein, Mrp2) was partially maintained in day 5 hepatocytes cultured in a sandwich configuration. Fluorescein-labeled taurocholate and carboxydichlorofluorescein were excreted into and concentrated in the bile canalicular lumen of day 5 sandwich-cultured hepatocytes, resulting in formation of fluorescent networks in standard buffer (intact bile canaliculi). Confocal microscopy studies demonstrated that 1) carboxydichlorofluorescein that had concentrated in the canalicular lumen was released into the incubation buffer in the presence of Ca(2+)-free buffer (disrupted bile canaliculi), and 2) rhodamine-dextran, an extracellular space marker, was only able to diffuse into the canalicular lumen in the presence of Ca(2+)-free buffer. The cumulative uptake of [(3)H]taurocholate in day 5 sandwich-cultured hepatocytes was significantly higher in standard buffer compared with Ca(2+)-free buffer, due to accumulation of taurocholate in canalicular spaces. When [(3)H]taurocholate was preloaded in the day 5 sandwich-cultured hepatocytes, taurocholate efflux was greater in Ca(2+)-free compared with standard buffer. The biliary excretion index of taurocholate, equivalent to the percentage of retained taurocholate in the canalicular networks, increased from approximately 8% at day 0 to approximately 60% at day 5 in sandwich-cultured hepatocytes. In summary, hepatocytes cultured in a collagen-sandwich configuration for up to 5 days establish intact canalicular networks, maintain Mrp2, reestablish polarized excretion of organic anions and bile acids, and represent a useful in vitro model system to investigate the hepatobiliary disposition of substrates.