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  • 1
    Electronic Resource
    Electronic Resource
    Differential localization of organic cation transporters rOCT1 and rOCT2 in the basolateral membrane of rat kidney proximal tubules (2000)
    Springer
    Histochemistry and cell biology 114 (2000), S. 175-180 
    Details
    ISSN: 1432-119X
    Keywords: Organic cation transporter rOCT1 rOCT2 Kidney Proximal tubule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. Organic cation transporters play an important role in the secretion of cationic drugs as well as endogenous cationic metabolites in the renal tubules. Immunoblotting showed the presence of organic cation transporter proteins, rOCT1 and rOCT2, in the rat kidney. By immunofluorescence microscopy, rOCT1 was shown to be concentrated in the proximal tubules in the renal cortex. rOCT2, on the other hand, was rich in the proximal tubules in the outer stripe of the outer medulla. Confocal microscopy revealed that both rOCT1 and rOCT2 were localized to the basolateral membranes of these tubule cells. These findings directly show that rOCT1 and rOCT2 are basolateral membrane proteins and are differentially distributed along the proximal tubules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004180000186
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  • 2
    Electronic Resource
    Electronic Resource
    Peptide Transporter in the Rat Small Intestine: Ultrastructural Localization and the Effect of Starvation and Administration of Amino Acids (1999)
    Springer
    Journal of molecular histology 31 (1999), S. 169-174 
    Details
    ISSN: 1573-6865
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Peptide transporter-1 is a H+/peptide cotransporter responsible for the uptake of small peptides and peptide-like drugs, and is present in the absorptive epithelial cells of the villi in the small intestine (duodenum, jejunum, and ileum). It has been localized to the apical microvillous plasma membrane of the absorptive epithelial cells of the rat small intestine using the immunogold electron microscopic technique. Digital image analysis of the jejunum revealed that the transporter protein was abundant at the tip of the villus and that the amount decreased from the tip of the villus to its base. The effect of dietary administration of amino acids and starvation on the expression of PepT1 in the jejunum was examined by immunoblotting and image analysis of immunofluorescence. Starvation markedly increased the amount of peptide transporter present, whereas dietary administration of amino acids reduced it. The gradient of the transporter protein along the crypt-villus axis was maintained under either condition. These observations show that it is specific to the microvillous plasma membrane and that its expression is regulated by the nutritional condition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003515413550
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  • 3
    Electronic Resource
    Electronic Resource
    Decreased Cellular Toxicity of Neomycin in a Clonal Cell Line Isolated from LLC-PK1 (1993)
    Springer
    Pharmaceutical research 10 (1993), S. 573-576 
    Details
    ISSN: 1573-904X
    Keywords: aminoglycoside nephrotoxicity ; apical membrane enzymes ; cell cloning ; neomycin-resistance ; kidney epithelial cell line
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract We have previously shown in LLC-PK1 cells, that apical membrane enzyme activity was inhibited by aminoglycoside antibiotics (Am. J. Physiol. 254, C251-C257, 1988). In the present study, the relationship between the lethal cytotoxic effect of aminoglycoside and its effect on apical membrane enzyme was examined by establishing aminoglycoside resistant cells. A clonal cell line, LLC-PK1/NRa3, was isolated from parent LLC-PK1 cells in the presence of neomycin. Neomycin inhibited colony formation and increased the number of floating dead cells in parent LLC-PK1 cultures. In contrast, these cytotoxic effects of neomycin were negligible or less pronounced in NRa3 cells, indicating that NRa3 cells were more resistant to neomycin compared with the parent cells. The inhibitory effect of neomycin on apical enzyme activity was significantly weaker in NRa3 cells than in the parent cells. These results suggest that a common mechanism is involved in the aminoglycoside-induced reductions in the apical enzyme activity and in cell viability of LLC-PK1 cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018954204094
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  • 4
    Electronic Resource
    Electronic Resource
    Simulation for population analysis of Michaelis-Menten elimination kinetics (1995)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 23 (1995), S. 205-216 
    Details
    ISSN: 1573-8744
    Keywords: Michaelis-Menten kinetics ; NONMEM ; population pharmacokinetics ; statistical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A simulation study was conducted to compare the cost and performance of various models for population analysis of the steady state pharmacokinetic data arising from a one-compartment model with Michaelis-Menten elimination. The usual Michaelis-Menten model (MM) and its variants provide no estimate of the volume of distribution, and generally give poor estimates of the maximal elimination rate and the Michaelis-Menten constant. The exact solution to the Michaelis-Menten differential equation (TRUE) requires a precise analysis method designed for estimation of population pharmacokinetic parameters (the first-order conditional estimation method) and also considerable computational time to estimate population mean parameters accurately. The one-compartment model with dose-dependent clearance (DDCL), in conjunction with the first-order conditional estimation or Laplacian method, ran approximately 20-fold faster than TRUE and gave accurate population mean parameters for a drug having a long biological half-life relative to the dosing interval. These findings suggest that the well-known MM and its variants should be used carefully for the analysis of blood concentrations of a drug with Michaelis-Menten elimination kinetics, and that TRUE, in conjunction with a precise analysis method, should be considered for estimating population pharmacokinetic parameters. In addition, DDCL is a promising alternative to TRUE with respect to computation time, when the dosing interval is short relative to the biological half-life of a drug.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02354272
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  • 5
    Electronic Resource
    Electronic Resource
    Kinetic Analysis of p-Aminohippurate Transport in the OK Kidney Epithelial Cell Line (2000)
    Springer
    Pharmaceutical research 17 (2000), S. 1155-1157 
    Details
    ISSN: 1573-904X
    Keywords: organic anion ; p-aminohippurate ; epithelial transport ; kinetic analysis ; opossum kidney (OK) cell line
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026478301483
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of Intestinal and Hepatic Metabolism on the Bioavailability of Tacrolimus in Rats (1998)
    Springer
    Pharmaceutical research 15 (1998), S. 1609-1613 
    Details
    ISSN: 1573-904X
    Keywords: tacrolimus ; bioavailability ; metabolism ; intestine ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Tacrolimus, an immunosuppressive agent, has poor and variable bioavailability following oral administration in clinical use. We investigated the contribution of intestinal metabolism to the first pass effect of tacrolimus in rats. Methods. Tacrolimus was administered intravenously, intraportally or intraintestinally to rats. Blood samples were collected over a 240-min period, and blood tacrolimus concentrations were measured. The extraction ratios of tacrolimus in the intestine and liver were investigated. In addition, the metabolism of tacrolimus in the everted sacs of the small intestine was examined. Results. The rate of absorption of tacrolimus in the intestine was rapid, and tacrolimus was almost completely absorbed after intestinal administration. The bioavailability of tacrolimus was about 40% and 25% after intraportal and intraintestinal administration, respectively, indicating that tacrolimus is metabolized in both the intestine and the liver. In addition, tacrolimus was significantly metabolized in the everted sacs of the rat intestine. Conclusions. The present study suggested that the metabolism of tacrolimus in the intestine contributes to its extensive and variable first pass metabolism following the oral administration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011967519752
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  • 7
    Electronic Resource
    Electronic Resource
    Modulation of Organic Cation Transport and Lipid Fluidity by Benzyl Alcohol in Rat Renal Brush-border Membranes (1996)
    Springer
    Pharmaceutical research 13 (1996), S. 1069-1072 
    Details
    ISSN: 1573-904X
    Keywords: renal transport ; organic cation ; membrane fluidity ; brush-border membrane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Organic cations are actively transported in renal brush-border membranes (BBM) by the H+/organic cation antiport system. In the present study, we investigated the relationship between membrane fluidity and organic cation transport in the BBM. Methods. The effects of benzyl alcohol, a membrane fluidizing agent, on the organic cation tetraethylammonium (TEA) uptake were studied using renal BBM vesicles isolated from rat kidney. BBM fluidity was assessed by fluorescence polarization technique. Results. H+ gradient-dependent uptake of TEA in BBM vesicles was inhibited by benzyl alcohol in a dose-dependent manner, with an apparent half inhibitory concentration of 18mM. The decrease in fluorescence anisotropy of l,6-diphenyl-l,3,5-hexatriene in BBM, which represents the increase in membrane fluidity, was correlated with the decrease in TEA transport activity. The dissipation rate of H+ gradient, a driving force for organic cation transport in BBM, was increased by benzyl alcohol. In addition, H+ gradient-independent TEA-TEA exchange was also inhibited by benzyl alcohol. These findings indicate that benzyl alcohol inhibits the uptake of TEA by affecting the intrinsic activity of the organic cation transporter and the H+ gradient dissipation rate. Conclusions. The membrane fluidity should be an important determinant for organic cation transport in renal BBM.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016066926269
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of Cyclosporin Analogues and FK506 on Transcellular Transport of Daunorubicin and Vinblastine via P-glycoprotein (1996)
    Springer
    Pharmaceutical research 13 (1996), S. 1073-1077 
    Details
    ISSN: 1573-904X
    Keywords: P-glycoprotein ; cyclosporins ; FK506 ; daunorubicin ; vinblastine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. P-glycoprotein-mediated transcellular transport of anticancer agents and the inhibitory effect of cyclosporin analogs and FK506 were investigated. Methods. The transcellular transport of daunorubicin and vinblastine by monolayers of LLC-GA5-COL150 cells which overexpressed P-glycoprotein was measured in the presence and absence of cyclosporins or FK506. Results. Cyclosporins and FK506 inhibited P-glycoprotein-mediated transport of daunorubicin and vinblastine in the order of cyclosporin D, dihydrocyclosporin D 〉 cyclosporin A 〉 FK506 〉 cyclosporin C, dihydrocyclosporin C. The intracellular accumulation of the anticancer agents was highly associated with the transporting function of P-glycoprotein. The inhibitory effect of cyclosporin D was concentration-dependent. The inhibitory effect of the modulators on P-glycoprotein was not correlated with the immunosuppressive activity, but was correlated with their lipophilicity. Conclusions. In the transcellular transport system, lipophilicity may be one of the determinants for the inhibitory effect of various multidrug resistance modulators on the P-glycoprotein-mediated transport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016019010339
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  • 9
    Electronic Resource
    Electronic Resource
    Transport Characteristics of Ceftibuten, a New Cephalosporin Antibiotic, via the Apical H+/Dipeptide Cotransport System in Human Intestinal Cell Line Caco-2: Regulation by Cell Growth (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 1483-1487 
    Details
    ISSN: 1573-904X
    Keywords: cephalosporin antibiotics ; H +/dipeptide cotransporter ; Caco-2 cells ; cell growth ; intestinal absorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The intestinal epithelial cell line Caco-2 possesses the H+/ dipeptide cotransport system responsible for uptake of oral cephalosporins. In this study, the transport characteristics of ceftibuten were examined from the viewpoint of cell growth in the Caco-2 cells. Methods. The uptake of cephalosporins by Caco-2 cell monolayers grown on plastic dishes was measured and analyzed kinetically. Results. The uptake of ceftibuten was increased by lowering pH of the incubation medium and was inhibited by excess dipeptide. The transport activity of ceftibuten was dependent on the duration of culture, being maximal on the 14th day after inoculation. Kinetic analysis revealed that the development of ceftibuten uptake was due to not only a decrease in Km but also to an increase in Vmax value. Conclusions. The uptake of ceftibuten is mediated by the apical H+/ dipeptide cotransport system which is regulated by cell growth and/or differentiation in the Caco-2 cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016235404598
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  • 10
    Electronic Resource
    Electronic Resource
    Transepithelial Transport of Diphenhydramine Across Monolayers of the Human Intestinal Epithelial Cell Line Caco-2 (2000)
    Springer
    Pharmaceutical research 17 (2000), S. 539-545 
    Details
    ISSN: 1573-904X
    Keywords: Caco-2 cells ; diphenhydramine ; transepithelial transport ; intestinal absorption ; intestinal secretion ; organic cation transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The transepithelial transport characteristics of theantihistamine, diphenhydramine, were studied in human intestinal Caco-2 cellmonolayers to elucidate the mechanisms of its intestinal absorption. Methods. The transepithelial transport and the cellular accumulationof diphenhydramine were measured using Caco-2 cell monolayersgrown in Transwell chambers. Results. The transepithelial transport of diphenhydramine from theapical to basolateral side was saturable, and the flux and cellularaccumulation of diphenhydramine were dependent on the apicalextracellular pH (pH 7.4 〉 6.5 〉 5.5). Transport and accumulation ofdiphenhydramine from the apical side were inhibited by anotherantihistamine, chlorpheniramine, while typical substrates for the renal organiccation transport system such as tetraethylammonium, cimetidine andguanidine had no effect. The transepithelial transport and cellularaccumulation of diphenhydramine from the basolateral side were alsopH-dependent and inhibited by chlorpheniramine. In addition, intracellulardiphenhydramine preloaded was preferentially effluxed to the apicalside, suggesting the involvement of the secretory pathway indiphenhydramine transport. Furthermore, diphenhydramine uptake from boththe apical and basolateral sides was stimulated by preloadingmonolayers with chlorpheniramine (trans-stimulation effect). Conclusions. Transepithelial transport of diphenhydramine acrossCaco-2 cells is mediated by pH-dependent, specific transport systemsthat exist in both the apical and basolateral membranes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007560731098
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