Hepatocellular uptake of sulfobromophthalein and bilirubin is selectively inhibited by an antibody to the liver plasma membrane sulfobromophthalein/bilirubin binding protein.
To clarify sulfobromophthalein (BSP) and bilirubin uptake mechanisms, isolated rat hepatocytes were incubated with [35S]BSP. The initial uptake velocity (V0), determined from the first, linear portion of the cumulative uptake curve, was saturable (Michaelis constant [Km] = 6.2 +/- 0.5 microM; Vmax = 638 +/- 33 pmol X min-1 per 10(5) hepatocytes), maximal at 37 degrees C and pH 7.4, and competitively inhibited by bilirubin, but not by taurocholate, cholate, or oleate. Preloading with unlabeled BSP led to trans-stimulation of V0. Sodium substitution or pretreatment of hepatocytes with ouabain or metabolic inhibitors had no effect on V0; trypsin reduced V0 by 39% (P less than 0.001). A rabbit antiserum to the rat liver plasma membrane (LPM)-BSP/bilirubin binding protein selectively reduced V0 of 5 microM [35S]BSP and [14C]bilirubin by 41 and 42%, respectively (P less than 0.01); uptakes of [3H]oleate, [3H]cholate and [3H]taurocholate were not affected. Hence, the LPM-BSP/bilirubin binding protein plays a role in the carrier-mediated uptake of BSP and bilirubin by hepatocytes.
D000818:Animals; D001663:Bilirubin / Q000378:metabolism* / Q000494:pharmacology; D002352:Carrier Proteins / Q000276:immunology / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D007106:Immune Sera / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013448:Sulfobromophthalein / Q000378:metabolism*
D002352:Carrier Proteins; D007106:Immune Sera; C488927:bilirubin binding protein, rat; D013448:Sulfobromophthalein; D001663:Bilirubin