Characterization of Renal Brush-Border and Basolateral Membrane Transporters for Organic Cations

Wright, Stephen H.

doi:10.1159/000154800

Cited by 4 publications

(5 citation statements)

References 41 publications

(61 reference statements)

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“…Finally, the EC50 values for cimetidine and choline at the HV organic cation exchanger of the luminal mem brane of proximal tubules were reported to be 0.07 [7] and 21 mM [12], respectively, which is identical to the results found in our study (0.05 mM for cimetidine and 20 mM for cho line). The HVorganic cation transport system is electroneutral [1,3]; thus, uptake of ASP+ via this system should be independent of membrane voltage. As demonstrated here cell depolarization caused no change in cellular pH: however, it decreased the ASP+ accumu lation.…”

Section: Discussionmentioning

confidence: 99%

“…Three different transporters for organic cat ions have been identified in the proximal tubule so far [1][2][3]. An electrogenic organic cation transporter was identified in the basolateral membrane of this nephron segment [4][5][6], whereas in the luminal membrane two dif ferent transporters have been reported, an clcctroneutral HVorganic cation exchanger and an electrogenic choline transporter [7][8][9][10], Transport via these proteins is influenced by several cationic substrates inducing flux coupling phenomena such as cis-inhibition, trans-stimulation and trans-inhibition [11][12][13].…”

Section: Introductionmentioning

confidence: 99%

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Characterisation of Organic Cation Transport across the Apical Membrane of Proximal Tubular Cells with the Fluorescent Dye 4-Di-1-ASP

Stachon¹,

Hohage²,

Feidt³

et al. 1997

Cell Physiol Biochem

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Recently, we introduced a new method to monitor organic cation transport using the fluorescent dye 4-(4-dimethylaminostyryl)-N-methylpyridinium (ASP⁺). We now examined properties of ASP⁺ uptake across the apical membrane of proximal tubular cells (LLC-PK₁ and IHKE1) with this new method and compared the results with characteristics of organic cation transport obtained in transport studies using radio-labeled substrates. Cimetidine and choline inhibited ASP⁺ accumulation in LLC-PK₁ cells with maximal inhibitions of 51 ± 5% (n = 6, at 1 mM) and 45 ± 14% (n = 6, at 50 mM), respectively. TMA⁺, TEA⁺ and THA⁺ showed bell-shaped concentration-response curves in LLC-PK₁ and IHKE1 cells. Maximal inhibition was achieved in LLC-PK₁ cells with 10 mMTMA⁺ (53 ± 4%, n = 6), 5 mMTEA⁺ (64 ± 4%, n = 4) and 10 µMTHA⁺ (97 ± 5%, n = 6) and in IHKE1 cells with > 50 mMTMA⁺ (51 ± 8%, n = 6), 1 mMTEA⁺ (53 ± 12%, n = 6) and 5 µMTHA⁺(100 ± 1%, n = 6). Higher concentrations of these cations led to a reduction of the inhibitory effect. ASP⁺ accumulation in LLC-PK₁ cells was reduced at pH 6.0 by 60 ± 5% (n = 7) and increased at pH 8.4 by 18 ± 6% (n = 6). Membrane depolarization induced by increases in the extracelluar K⁺ concentration to 50 or 145 mMled to a reduction of the ASP⁺ accumulation in LLC-PK₁ cells by 27 ± 7% (n = 5) or 37 ± 6% (n = 5), respectively. The data of this study demonstrate that ASP⁺ accumulation across the apical membrane of LLC-PK₁ and IHKE1 cells measured fluorimetrically has properties comparable to those reported for the H⁺/organic cation exchanger described for the luminal membrane of the proximal tubule.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Characterisation of Organic Cation Transport across the Apical Membrane of Proximal Tubular Cells with the Fluorescent Dye 4-Di-1-ASP

Stachon¹,

Hohage²,

Feidt³

et al. 1997

Cell Physiol Biochem

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“…Addition of lamivudine was found to inhibit the transient increase in TEA uptake. The uptake of TEA by BBMV under an outward H gradient is known to be mediated by an H aorganic cation anti-port system (Takano et al 1984;Wright 1996;Pritchard & Miller 1997), indicating that lamivudine might inhibit transport of organic cations by the anti-port system. As found previously, the stimulated uptake of TEA by BBMV under an outward H gradient was reduced signi®cantly by cimetidine, a representative cationic drug, but not by probenecid, a representative anionic drug (Takano et al 1985;Grif®ths et al 1992).…”

Section: Takatoshi Takubo Et Almentioning

confidence: 99%

“…At an early stage this uptake was reduced by lamivudine. TEA uptake by BLMV was reported to involve a carrier-mediated system and it was suggested that lamivudine might inhibit transport of organic cations by this system (Takano et al 1984;Wright 1996;Pritchard & Miller 1997). The uptake of TEA by BLMV at an early stage was reduced signi®cantly by the presence of cimetidine or trimethoprim; the IC50 of trimethoprim was fourfold (approx.)…”

Section: Takatoshi Takubo Et Almentioning

confidence: 99%

“…Renal tubular excretion would consist of two processes, in¯ux at the basolateral membrane and ef¯ux at the brush-border membrane of the renal tubule epithelium. In¯ux and ef¯ux of organic cations mainly involve electrogenic-facilitated diffusion and H ±organic cation exchange, respectively (Wright 1996;Pritchard & Miller 1997). It has also been suggested that competitive inhibition of these processes, by the concomitant use of other cationic drugs, would reduce their renal clearance (Bendayan 1996;Bonate et al 1998).…”

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Effect of Lamivudine on Uptake of Organic Cations by Rat Renal Brush-Border and Basolateral Membrane Vesicles

Takubo¹,

Kato²,

Kinami³

et al. 2000

Journal of Pharmacy and Pharmacology

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The effect of lamivudine on uptake of a representative organic cation, tetraethylammonium (TEA), by rat renal brush-border membrane vesicles (BBMV) and basolateral membrane vesicles (BLMV) has been investigated. The pH-driven uptake of TEA by BBMV (pHin = 6.0, pHout = 7.5) was inhibited by lamivudine. The IC50 value (concentration resulting in 50% inhibition) for the concentration-dependent effect of lamivudine on TEA uptake by BBMV after 30 s was 2668 microM whereas IC50 values for cimetidine and trimethoprim were < 2.5 microM and < 25 microM, respectively. The early uptake of TEA by BLMV was also reduced significantly by lamivudine. The IC50 value for the concentration-dependent effect of lamivudine on uptake of TEA by BLMV at 30 s was > 25 mM, whereas the IC50 values for cimetidine and trimethoprim were 2116 microM and 445 microM, respectively. These findings suggest that compared with other cationic drugs, such as trimethoprim and cimetidine, lamivudine is a weak inhibitor of organic cation transport into the tubules by the brush-border and basolateral membranes of renal epithelial cells. It is unlikely lamivudine will have any significant effect on the excretion of co-administered cationic drugs by the renal tubules.

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Influence of substrate structure on turnover of the organic cation/H + exchanger of the renal luminal membrane

Wright

Wunz

1998

Pfl�gers Archiv European Journal of Physiology

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We examined the influence of organic cation (OC) structure on the rate of turnover of the OC/H+ exchanger in rabbit renal brush-border membrane vesicles (BBMV). The rate of efflux of [14C]tetraethylammonium ([14C]TEA) from BBMV, measured in the presence of an inwardly directed chemical gradient for test agent, provided an indirect measure of activity of the OC/H+(OC) exchanger. The trans-stimulation of [14C]TEA efflux from BBMV was a saturable function of increasing extravesicular concentration of both unlabeled TEA and tetramethylammonium (TMA), with an apparent Michaelis constant (Kt) for the interaction of these compounds with the OC/H+(OC) exchanger of 25 microM and 1 mM, respectively. The effect on [14C]TEA efflux of saturating extravesicular concentrations of a series of n-tetraalkylammonium compounds was examined. Whereas the short-chain compounds TMA and TEA markedly stimulated [14C]TEA efflux (by 830% and 690%, respectively), the long-chain compounds tetrapropylammonium and tetrabutylammonium were less effective, increasing efflux by only 40% and 120%, respectively. When the exchanger was saturated with tetrapentylammonium, mediated efflux of [14C]TEA was reduced. Increasing alkyl chain length was also correlated with an increase in the inhibitory effect (as measured by the apparent inhibition constant, Ki, or the IC50 value) that these compounds had against transport of [14C]TEA by the OC/H+(OC) exchanger; i.e., there was a correlation between decreasing IC50 and decreasing turnover of the OC/H+(OC) exchanger. This same correlation was observed for a broader set of test agents of diverse molecular structure, including a series of n-tetraalkylammonium and -phosphonium compounds and the OCs, choline, N1-methyl nicotinamide, 1-methyl-4-phenylpyridinium, and amiloride. Because high affinity of substrates for the OC/H+(OC) exchanger is correlated with increasing substrate hydrophobicity, we conclude that the interaction of hydrophobic OCs with the renal OC/H+(OC) exchanger results in the formation of a substrate-exchanger complex that has a comparatively low rate of turnover.

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Characterization of Renal Brush-Border and Basolateral Membrane Transporters for Organic Cations

Cited by 4 publications

References 41 publications

Characterisation of Organic Cation Transport across the Apical Membrane of Proximal Tubular Cells with the Fluorescent Dye 4-Di-1-ASP

Characterisation of Organic Cation Transport across the Apical Membrane of Proximal Tubular Cells with the Fluorescent Dye 4-Di-1-ASP

Effect of Lamivudine on Uptake of Organic Cations by Rat Renal Brush-Border and Basolateral Membrane Vesicles

Influence of substrate structure on turnover of the organic cation/H + exchanger of the renal luminal membrane

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