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  • 1
    Electronic Resource
    Electronic Resource
    Conductance Change in Phospholipid Bilayer Membrane by an Electroneutral Ionophore, Monensin (1995)
    s.l. : American Chemical Society
    Biochemistry 34 (1995), S. 3455-3460 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00010a038
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  • 2
    Electronic Resource
    Electronic Resource
    Activation Energy for Permeation of Phosphonium Cations through Phospholipid Bilayer Membrane (1994)
    s.l. : American Chemical Society
    Biochemistry 33 (1994), S. 4312-4318 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00180a027
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  • 3
    Electronic Resource
    Electronic Resource
    Nucleosides and Nucleotides. 141. Chemical Stability of a New Antitumor Nucleoside, 2'-C-Cyano-2'-deoxy-1-.beta.-D-arabino-pentofuranosylcytosine (CNDAC) in Alkaline Medium: Formation of 2'-C-Cyano-2'-deoxy-1-.beta.-D-ribo-pentofuranosylcytosine (CNDC) and Its Antitumor Activity (1995)
    s.l. : American Chemical Society
    Journal of medicinal chemistry 38 (1995), S. 3391-3397 
    Details
    ISSN: 1520-4804
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jm00017a023
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  • 4
    Electronic Resource
    Electronic Resource
    Doxorubicin-efflux pump in Haloferax voleanii is energized by ATP (1996)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 139 (1996), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Haloferax voleanii acquires resistance to doxorubicin, and this acquisition involves an active extrusion of lipophilic drugs. We have investigated what this drug-efflux transporter utilizes as an energy source to expel drugs from the cells. The efflux activity was estimated from the direct measurement of drug efflux rate and from the steady-state level of drug accumulation. Cells treated with N,N′-dicyclohexyl-carbodiimide showed a significant decrease in the efflux activity without changing membrane potential and Na+-electrochemical potential. This efflux system is energized by ATP but not by either a H+- or Na+-electrochemical potential difference.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1996.tb08183.x
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  • 5
    Electronic Resource
    Electronic Resource
    Kinetic analysis of the dose-dependent hepatic handling of 1-anilino-8-naphthalene sulfonate in rats (1990)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 18 (1990), S. 313-333 
    Details
    ISSN: 1573-8744
    Keywords: hepatic transport ; 1-anilino-8-naphthalene sulfonate (ANS) ; dose dependency ; saturable tissue binding ; organic anions ; cytosolic protein ; nonlinear pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The dose dependency in the hepatic transport of an anionic fluorescent dye, 1-anilino-8-naphthalene sulfonate (ANS), was investigated by measuring the plasma disappearance and biliary excretion in rats. Bulk of the administered ANS distributed into the liver at 10 min after iv bolus injection. The plasma disappearance curves of ANS were then kinetically analyzed based on a two-compartment model, in which the ligand is eliminated only from the peripheral compartment (liver compartment). The total body clearance (CLtot) decreased with increasing dose of ANS. That is, the values of CLtot were 4.06 and 1.98 ml/min/per kg at the doses of 3 and 100 Μmol/kg, respectively. The clearances of the uptake and sequestration processes (CLup and CLseq, respectively) for a total ligand were constant irrespective of dose, while the efflux clearance (CLeff) for a total ligand was increased by twofold with increasing dose. A mechanism for the increase in the CLeff value might be explained by a saturation of the ANS binding to the intracellular proteins. The hepatocellular distribution and the binding of ANS to cytosolic proteins were then determined. ANS mainly distributed to the cytosol fraction, and the unbound fraction in the cytosol increased from approximately 0.04 to 0.09 when the cytosolic concentrations of ANS increased from 40 to 900 ΜM, respectively. In,spite of such increase in the unbound fraction in the cytosol, the CLseq values remained unchanged with increasing dose, suggesting that the saturation of sequestration clearance for unbound ANS might occur. Furthermore, the plasma disappearance curves of ANS at various doses were simultaneously analyzed based on three nonlinear kinetic models: Model I is a model incorporating both saturable intracellular binding and saturable sequestration; Model II is a model incorporating only saturable intracellular binding; Model III is the model incorporating only saturable sequestration. Goodness- of- fit evaluated by AIC value was best for Model I. Taken together, the nonlinearity in the plasma clearance of ANS was confirmed to be attributed to saturation of both its binding to cytosolic proteins and sequestration process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01062271
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  • 6
    Electronic Resource
    Electronic Resource
    Comparison of the Hepatic Uptake Clearances of Fifteen Drugs with a Wide Range of Membrane Permeabilities in Isolated Rat Hepatocytes and Perfused Rat Livers (1993)
    Springer
    Pharmaceutical research 10 (1993), S. 434-440 
    Details
    ISSN: 1573-904X
    Keywords: hepatic uptake clearance ; rat hepatocytes ; perfused rat liver ; unstirred water layer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The hepatic uptake clearances of 15 ligands with a wide range of permeabilities were determined in rats using two techniques: centrifugal filtration with isolated hepatocytes and the multiple indicator dilution (MID) method with isolated perfused livers. Some of the uptake clearance values were taken from the literature. Uptake clearance values obtained from isolated hepatocytes were extrapolated to that per gram liver (PS inf, cell), assuming that 1 g of liver has 1.3 × 108 cells. The values of PS inf, cell varied from approximately 0.1 to 72 (mL/min/g liver). The values of PS inf, cell were similar to those (PS inf,MID) determined by the MID method for ligands with uptake clearances below approximately 1 mL/min/g liver. However, for the ligands with larger uptake clearances, the PS inf, MID values were lower than the PS inf,cell values and appeared to reach an upper limit (approx. 15–20 mL/min/g liver). The PSinf,cell values of 1-propranolol, tetraphenylphosphonium (TPP+), and diazepam were 72, 43, and 22 mL/min/g liver, respectively, whereas their uptake clearances (PS inf,MID) determined by the MID method were 4 to 10 times lower. One of the possible mechanisms for this discrepancy is that an unstirred water layer, which may exist in Disse's space in isolated perfused livers (and probably under in vivo condition), limits the hepatic uptake rate of ligands with extremely high membrane permeabilities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018952709120
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of a diffusional barrier to a metabolite across hepatocytes on its kinetics in “enzyme-distributed” models: A computer-aided simulation study (1987)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 15 (1987), S. 399-421 
    Details
    ISSN: 1573-8744
    Keywords: diffusional barrier ; hepatic extraction ; enzyme-distributed model ; metabolite kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of a diffusional barrier to a metabolite between the blood and hepatocytes on elimination kinetics of formed and preformed metabolites was predicted under various enzymic distributions in the liver by computer- aided simulation. Sequential metabolism by which the primary metabolite (MI) is generated from the parent drug (D) and further metabolized to the terminal metabolite (MII) by enzymes A and B, respectively, was chosen for the simulation. Moreover, four models of enzymic distribution patterns were defined with regard to the hepatic blood flow path. The extraction ratios for the preformed and formed metabolites (designated as Em and Ep→m, respectively) were simulated by varying both the average intrinsic clearance of enzyme B ( $$\overline {CL_{int,B} }$$ ) and the permeability of hepatocytes for MI ( $$\overline {P_m }$$ ), while keeping the average intrinsic clearance of enzyme A ( $$\overline {CL_{int,A} }$$ ) equal to hepatic blood flow (Q). When a rapid equilibrium of MI between the blood and hepatocytes held, i.e., $$\overline {P_m }$$ was large relative to Q, Em was equal to or higher than Ep→m for all models, as previously shown by Pang and Stillwell. By contrast, it was found that when a diffusional barrier for MI existed, i.e., $$\overline {P_m }$$ was small relative to Q, Em was equal to or lower than Ep→m. Furthermore, it was observed that the smaller $$\overline {P_m }$$ became, the larger the difference between Em and Ep→m became. We further simulated the effect of the intrinsic clearance ( $$\overline {CL_{int,C} }$$ ) for a metabolic pathway, which competes for that by enzyme A. on the E p→m value. In the model assuming even distribution of all the enzymes along the flow path, irrespective of the $$\overline {CL_{int,C} }$$ value, a similar effect of $$\overline {P_m }$$ on Ep→m was observed when the $$\overline {P_m }$$ value was relatively small ( $$\overline {P_m }〈 Q$$ ). By contrast, in the case of uneven enzymic distributions of enzymes A and B, the effect of the $$\overline {CL_{int,C} }$$ value on the relationship between Pm and Ep→m occurred to some extent. From these simulations, it was concluded that lower membrane permeability ( $$\overline {P_m }$$ ) both diminishes the entry of preformed metabolite into the hepatocytes and accelerates the removal of intracellularly formed metabolite (through sequential metabolism) by diminishing its efflux, yielding lower Em than Ep→m. When $$\overline {P_m }$$ becomes small ( $$\overline {P_m }〈 1/10Q$$ ), these mechanisms for lower Em than Ep→m predominate over other mechanisms such as the presence of a competing metabolic route and uneven distribution of enzymes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01066521
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  • 8
    Electronic Resource
    Electronic Resource
    Kinetics of hepatic transport of 4-methylumbelliferone in rats. Analysis by multiple indicator dilution method (1987)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 15 (1987), S. 25-38 
    Details
    ISSN: 1573-8744
    Keywords: Hepatic transport ; 4-methylumbelliferone (4-MU) ; multiple indicator dilution (MID) method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Hepatic elimination of 4-methylumbelliferone (4MU), which has been used as a model compound for conjugative metabolism, was studied by means of a multiple indicator dilution (MID) method in the isolated perfused rat liver. Using this method, three intrinsic hepatic clearances, CL int,inf , CL int,eff, and CL int,seq, which represent the influx, efflux, and sequestration processes, respectively, were obtained. When the dose was increased from a low dose (50 μg/rat liver) to a high dose (3000 μg/rat liver), the hepatic availability of 4MU increased from 0.11 to 0.73. With increasing dose, the CL int,eff value increased approximately two times, while the CL int,seq value decreased to approximately one-third. The remarkable dose dependence of hepatic availability was due to nonlinearity in both CL int,eff and CL int,seq values. However, the CLint,inf value was almost independent of dose. The dose-dependent change in CLint,seq might be explained by the saturation of conjugative metabolism of 4-MU, while the increase in the CL int,eff value with increasing dose might be partly explained by the nonlinear tissue binding of 4-MU, since the tissue unbound fraction determined by an ultrafiltration method using liver homogenate increased approximately 1.5 times at higher concentration of 4-MU compared to that at lower concentrations. In addition, based on a comparison of the individual intrinsic clearances, i.e., CL int,inf , CL int,eff, and CL int,seq, the major determining process of the apparent hepatic intrinsic clearance of 4MU is thought to be the sequestration process at the high dose. However, at the low dose, the membrane transport process (influx and efflux processes) as well as the sequestration process also determine the apparent hepatic intrinsic clearance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01062937
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