Hepatic uptake of bromosulfophthalein-glutathione in perfused Eisai hyperbilirubinemic mutant rat liver: a multiple-indicator dilution study.
ABSTRACT The hepatocellular uptake of the glutathione conjugate of bromosulfophthalein (BSPGSH) was examined in Eisai hyperbilirubinemic rats (EHBR; originating from Sprague-Dawley rats), which lacked the ATP-dependent canalicular transport for non-bile acid organic anions, a trend common to other mutant rat strains (TR- and GY, originating from Wistar rats). Single-pass perfused rat liver experiments were conducted with BSPGSH (26-257 microM) using the multiple indicator dilution technique. The steady-state extraction ratio of BSPGSH was close to zero due to lack of biliary excretion. After the introduction of a bolus dose containing vascular (51Cr-labeled red blood cells), interstitial (125I-labeled albumin and [14C]sucrose) and cellular space (D2O) indicators and [3H]BSPGSH into the portal vein, the outflow dilution profile of [3H]BSPGSH was found to display a protracted declining profile (tailing) at low input BSPGSH concentrations; the tail disappeared at higher BSPGSH concentrations. When data were fitted with the barrier-limited model of Goresky as used previously for BSPGSH for the Sprague-Dawley rat (SDR), model fitting was found to evoke an additional "deep pool" within the hepatocyte to account for the "tail" component. The deep pool became evident for the EHBR because biliary excretion of BSPGSH was absent and the rate of return from the deep pool was slow. The concentration of BSPGSH within the deep pool was estimated to be 12 +/- 8 times that in the cytosol. The binding of BSPGSH to EHBR S9 (effective binding concentration of 53 microM and a binding association constant KA of 2.4 x 10(4) M-1), however, was found to be lower than that of SDR S9 and could not account for the late-in-time data. The influx permeability-surface area product was concentration dependent and decreased from 0.27 to 0.01 ml.sec-1.g-1 with increasing BSPGSH concentration; the throughput component, or the portion of the dose that goes through the liver without entering the hepatocyte, increased with increasing concentration. The trends were characteristic of carrier-mediated transport and were similar to those found for the uptake of BSPGSH in SDR.
SourceAvailable from: tspace.library.utoronto.ca
[Show abstract] [Hide abstract]
ABSTRACT: A four-region (capillary plasma, endothelium, ISF, cell) multipath model was configured to describe the kinetics of blood-tissue exchange for small solutes in the lung, accounting for regional flow heterogeneity, permeation of cell membranes and through interendothelial clefts, and intracellular reactions. Serotonin uptake data from the Multiple Indicator Dilution "bolus sweep" experiments of Rickaby et al. (JAP 51: 405, 1981), Rickaby et al. (JAP 56:1170, 1984), and Malcorps et al. (JAP 57: 720, 1984) were analyzed to distinguish facilitated transport into the endothelial cells (EC) and the inhibition of tracer transport by non-tracer serotonin in the bolus of injectate from the free uninhibited permeation through the clefts into the interstitial fluid space. The permeability-surface area products, PS, for serotonin via the inter-EC clefts were about 0.3 ml/(g•min), low compared to the transporter-mediated maximum PS of 13 ml/(g•min), (with Km = ~ 0.3 μM and Vmax = ~ 4 nmol/(g•min)). The estimates of serotonin PS's for EC transporters from their multiple data sets were similar, and were influenced only modestly by accounting for the cleft permeability in parallel. The cleft PS estimates in these Ringer-perfused lungs are less than half of those for anesthetized dogs (Yipintsoi, Circ Res 39:523, 1976) with normal hematocrits, but are compatible with passive non-carrier-mediated transport observed later in the same laboratory (Dawson et al. Ann Biomed Eng 15: 217, 1987; Peeters et al. JAP 66:2328, 1989) The identification and quantitation of the cleft pathway conductance from these studies affirms the importance of the cleft permeation.AJP Lung Cellular and Molecular Physiology 05/2013; 305(1). DOI:10.1152/ajplung.00420.2012 · 4.04 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: This white paper provides a critical analysis of methods for estimating transporter kinetics and recommendations on proper parameter calculation in various experimental systems. Rational interpretation of transporter-knockout animal findings and application of static and dynamic physiologically based modeling approaches for prediction of human transporter-mediated pharmacokinetics and drug–drug interactions (DDIs) are presented. The objective is to provide appropriate guidance for the use of in vitro, in vivo, and modeling tools in translational transporter science.Clinical Pharmacology & Therapeutics 02/2013; 94(1). DOI:10.1038/clpt.2013.45 · 7.39 Impact Factor