TRANSPORT OF FLUORESCENT BILE-ACIDS BY THE ISOLATED-PERFUSED RAT-LIVER - KINETICS, SEQUESTRATION, AND MOBILIZATION

Hepatocyte transport of six fluorescent bile acids containing nitroben zoxadiazolyl (NBD) or a fluorescein derivative on the side chain was c ompared with that of natural bile acids using the single-pass perfused rat liver. Compounds were infused at 40 nmol/g liver min for 15 minut es; hepatic uptake and biliary recovery were measured; fractional extr action, intrinsic basolateral clearance, and sequestration (nonrecover y after 45 minutes of additional perfusion) were calculated. Fluoresce nt bile acids were efficiently extracted during the first 3 minutes (7 0%-97%), but net extraction decreased with time mostly because of regu rgitation into the perfusate. For cholylglycine and ursodeoxycholylgly cine (UDC-glycine), extraction was 94% to 99%, and regurgitation did n ot occur. Intrinsic hepatic clearance of fluorescent bile acids (2-7 m L/g liver min) was lower than that of cholylglycine (9.0 +/- 0.6; mean +/- SD) and UDC-glycine (21.4 +/- 0.4). Sequestration at 60 minutes w as 8% to 26% for fluorescent bile acids with a cholyl moiety (cholylgl ycylaminofluorescein [CGamF], cholyllysylfluorescein [C-L-F], cholyl-[ N epsilon-NBD]-lysine [C-L-NBD], and cholylaminofluores cein [CamF]), 32% for ursodeoxycholylaminofluorescein (UDCamF), and 88% for ursodeox ycholyl-(N epsilon-NBD)-lysine (UDC-L-NBD). Cholylglycine and UDC-glyc ine had <3% retention. Biliary secretion of sequestered UDCamF, but no t of UDC-L-NBD, was induced by adding dibutyryl cyclic adenosine monop hosphate (DBcAMP) to the perfusate, possibly by translocation to the c analiculus of pericanalicular vesicles containing fluorescent bile aci ds. Biliary secretion of UDC-L-NBD, but not of UDCamF, was induced by adding cholyltaurine or UDC-taurine, possibly by inhibition of binding to intracellular constituents or of transport into organelles. It is concluded that fluorescent bile acids are efficiently transported acro ss the basolateral membrane, but in contrast to natural conjugated bil e acids, are sequestered in the hepatocyte (UDC derivatives > cholyl d erivatives). Two modes of hepatic sequestration of fluorescent bile ac ids were identified. Fluorescent bile acids may be useful to character ize sequestration processes during bile acid transport through the hep atocyte.