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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
    Structural requirements for determining the substrate affinity of peptide transporters PEPT1 and PEPT2 (2000)
    Springer
    Pflügers Archiv 440 (2000), S. 679-684 
    Details
    ISSN: 1432-2013
    Keywords: α- or β-Carbonyl function Cyclic dipeptides Di- and tripeptides Peptide transporters Substrate affinity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. Peptide transporters PEPT1 and PEPT2 transport numerous compounds including small peptides, peptide-like drugs and nonpeptidic compounds such as valacyclovir. PEPT1 and PEPT2 show low and high affinity for most substrates, respectively, but β-lactam antibiotics without an α-amino group are the only known substrates that prefer PEPT1 to PEPT2. The aim of this study was to compare the recognition and affinity of various substrates between rat PEPT1 and rat PEPT2, and to determine the structural requirements influencing the substrate affinity. [14C]Glycylsarcosine uptake by PEPT1- or PEPT2-expressing transfectant was inhibited by di- and tripeptides, but not by amino acids, tetrapeptides or most cyclic dipeptides. All dipeptides and tripeptides examined showed more potent inhibition of [14C]glycylsarcosine uptake via PEPT2 than via PEPT1, irrespective of their charge and structure. Modification of the α-amino group of dipeptides reduced their substrate affinity to both transporters, as compared to unmodified dipeptides, but these dipeptides still showed potent inhibitory effects on PEPT2. Among the nonpeptidic substrates tested, only the eight-amino-octanoic acid displayed stronger inhibition of [14C]glycylsarcosine uptake in PEPT1 than in PEPT2. These findings suggest that α- or β-amino carbonyl function is the key structure responsible for the higher affinity for PEPT2 than for PEPT1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240000339
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  • 3
    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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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Transepithelial Transport of Levofloxacin in the Isolated Perfused Rat Kidney (2000)
    Springer
    Pharmaceutical research 17 (2000), S. 236-241 
    Details
    ISSN: 1573-904X
    Keywords: quinolones ; transport ; renal secretion ; isolated perfused kidney ; moment analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The transepithelial transport of levofloxacin was evaluatedin the isolated perfused kidney to investigate its renal secretorymechanisms. Methods. Levofloxacin was instantaneously administered into the renalartery together with inulin and Evans blue-labeled albumin, and thesingle-pass dilution curves of the renal venous and urinary outflowwere determined in the absence or presence of various compounds.Kinetic parameters were computed based on non-compartmentmoment analysis. Results. The ratio of fractional excretion to filtration fraction (FE/FF)for levofloxacin was 2.99 ± 0.18, indicating the involvement of tubularsecretion. In the presence of cimetidine and quinolones, the FE/FF oflevofloxacin was significantly decreased and the transepithelial meantransit time (¯Tcell) of levofloxacin was prolonged. The ¯Tcell showed anegative correlation with renal secretion of levofloxacin, while thevolume of distribution of levofloxacin showed no correlation. Conclusions. Transport on the brush-border membrane plays adetermining step in the renal secretion of levofloxacin, and cimetidineand quinolones interact with levofloxacin transport on thebrush-border membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007533817835
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  • 6
    Electronic Resource
    Electronic Resource
    N-terminal Halves of Rat H+/Peptide Transporters Are Responsible for Their Substrate Recognition (2000)
    Springer
    Pharmaceutical research 17 (2000), S. 15-20 
    Details
    ISSN: 1573-904X
    Keywords: peptide transporters ; chimeras ; intestinal absorption ; renal reabsorption ; β-lactam antibiotics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Peptide transporters PEPT1 and PEPT2 differ substantiallyin their substrate affinity and recognition. The aim of this study is todefine the structural domains which influence the functionalcharacteristics of both transporters Methods. Two kinds of chimeric peptide transporters (PEPT-N1C2and PEPT-N2C1) were constructed, and their functional characteristicswere compared with those of wild-type transporters in stabletransfectants. Results. PEPT-N1C2, the N-terminal half of rat PEPT1 and theC-terminal half of rat PEPT2, and the reciprocal chimera PEPT-N2C1were functionally expressed in LLC-PK1 cells. The pH-profiles of [14C]glycylsarcosine uptake by PEPT-N1C2 and PEPT-N2C1 were close tothose of PEPT1 and PEPT2, respectively. Substrate recognition forPEPT-N1C2 and PEPT-N2C1 was also similar to that of PEPT1 andPEPT2, respectively. However, substrate affinities for PEPT-N1C2were higher than those for PEPT1, although those for PEPT-N2C1 andPEPT2 were comparable. Conclusions. These results indicate that functional regions which areassociated with the extracellular pH changes and are responsible forsubstrate recognition of PEPT1 and PEPT2 may be located in theN-terminal halves of the proteins. In addition, it is suggested that thedomain to affect the substrate affinity exists in the C-terminal as wellas in the N-terminal half of rat PEPT2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007554105597
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