CANALICULAR RETENTION AS AN IN-VITRO ASSAY OF TIGHT JUNCTIONAL PERMEABILITY IN ISOLATED HEPATOCYTE COUPLETS - EFFECTS OF PROTEIN-KINASE MODULATION AND CHOLESTATIC AGENTS

A simple, fast method to evaluate acute changes of tight junctional pe rmeability in isolated hepatocyte couplets is proposed, The method con sists of the recording of the number of canalicular vacuoles able to r etain the previously accumulated fluorescent bile acid analogue cholyl -lysyl-fluorescein (CLF), as visualized by inverted fluorescent micros copy, following acute exposure to the compounds under study, The metho d was validated by (i) making a systematic documentation of the effect on CLF retention of a variety of hormonal modulators (vasopressin and phorbol esters), as well as several cholestatic (taurolithocholic aci d, cyclosporin A, and estradiol 17 beta-glucuronide) and hepatotoxic a gents (menadione, A23187, and t-butyl hydroperoxide), all known to aff ect biliary permeability in intact liver, and (ii) carrying out a comp arative analysis of the results obtained with those recorded using rap id canalicular access of horseradish peroxidase (HRP) as an alternativ e procedure. The compounds tested all decreased canalicular vacuolar r etention of CLF in a dose-dependent manner, Vasopressin- and phorbol e ster-induced decline in CLF retention were prevented by pretreatment w ith the protein kinase C inhibitors H-7 and staurosporine, thus confir ming a role for this enzyme in canalicular permeability regulation. A significant direct correlation (r = 0.934, p < 0.001) was obtained whe n the decrease in canalicular retention of CLF was compared with the i ncrement in the canalicular access of HRP. Image analysis revealed tha t cellular fluorescence was not increased following exposure to these compounds, suggesting a paracellular rather than transcellular route f or CLF egress. These results all support canalicular vacuolar retentio n of CLF as a suitable method to readily evaluate acute changes in tig ht junctional permeability in isolated hepatocyte couplets induced by physiological modulators or hepatotoxic agents. (C) 1997 Society of To xicology.