The hepatocellular transport of sulfobromophthalein-glutathione by clofibrate treated, perfused rat liver

Carrier-mediated uptake and excretion of bromosulfophthalein-glutathione in perfused rat liver: a multiple indicator dilution study

The hepatic removal of the glutathione conjugate of bromosulfophthalein (BSPGSH) was studied in the single-pass perfused rat liver with the multiple indicator dilution (MID) technique against various background concentrations of BSPGSH (20 to 214 mumol/L) over which nonlinear binding to both plasma (albumin) and tissue proteins with two classes of binding sites was found. A bolus containing 51Cr-labeled red blood cell (a vascular reference), [125I]albumin and [14C]sucrose (large and small molecular weight interstitial references, respectively), D2O (a cellular space reference), and [3H]BSPGSH was injected into the portal vein during steady-state. The eliminated fraction of dose, obtained by subtracting the survival fraction of [3H]BSPGSH in plasma from one, corresponded to the steady state extraction ratio (E) with bulk data, which declined from 0.74 +/- 0.04 to 0.27 +/- 0.01 with concentration. The major portion of the tracer outflow profile was a throughput component, which is the proportion of tracer that did not enter liver cells during its transit through the liver. The influx, efflux, and sequestration coefficients, evaluated with previously developed barrier-limited models, provided the corresponding influx (k1), efflux (k-1) and excretion (kseq) rate constants. Concentration-dependent influx (Vmax = 83 nmol min-1 g-1 and Km = 3.7 mumol/L), efflux (Vmax = 15 nmol min-1 g-1 and Km = 1.8 mumol/L), and excretion (Vmax = 94 nmol min-1 g-1 and Km = 1.8 mumol/L) were obtained for BSPGSH, when Km values are expressed in terms of the unbound concentrations. In these calculations, the observed unbound tissue concentration was not used for estimation of the Vmax and Km for efflux and excretion because of overestimation, because of the presence of highly concentrated BSPGSH in ductular elements present in liver homogenates; rather, the unbound tissue concentration was calculated from the influx, efflux, and removal rate coefficients. Because of carrier-mediated entry, the unbound tissue concentration does not equal the unbound plasma concentration, and kinetic parameters for BSPGSH excretion could be alternately estimated when the rate of excretion or net rate of loss of BSPGSH from plasma was regressed against the estimated tissue unbound concentration. This yielded a Vmax of 97 nmol min-1 g-1 and a Km of 3.6 mumol/L, values similar to those obtained from MID.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of clofibric acid on the turnover of the fatty acid-binding protein identified in cultured endothelial cells from bovine aorta

Several types of fatty acid-binding proteins are found in mammalian cells. Cultured endothelial cells from bovine aorta were shown to contain exclusively the cardiac-type fatty acid-binding protein (cFABP) with a mean concentration of 90 ng cFABP/mg extract protein. Only small variations were observed from passage to passage. In pulse-chase labeling experiments with L-[35S]methionine, a half-life of 4.0 d was measured for cFABP which is about two times longer than the average half-life of the extracted proteins. These data imply that in aortic endothelial cells cFABP is not subject to short-term regulation. However, addition of clofibric acid to the culture medium led to a shortening of the half-life of cFABP, which was compensated for by an increase in its biosynthesis. The turnover of the bulk of extract proteins remained unchanged when the cells were challenged with clofibric acid.