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Kenichi Inui - One of the best experts on this subject based on the ideXlab platform.
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Molecular mechanisms of organic Cation Transport in OCT2-expressing Xenopus oocytes.
Biochimica et Biophysica Acta, 1999Co-Authors: Masahiro Okuda, Yumiko Urakami, Hideyuki Saito, Kenichi InuiAbstract:Abstract The molecular mechanisms of organic Cation Transport by rat OCT2 was examined in the Xenopus oocyte expression system. When extracellular Na+ ions were replaced with K+ ions, uptake of tetraethylammonium (TEA) by OCT2-expressing oocytes was decreased, suggesting that TEA uptake by OCT2 is dependent on membrane potential. Kinetic analysis revealed that the decreased TEA uptake by ion substitution was caused at least in part by decreased substrate affinity. AcidifiCation of extracellular buffer resulted in decreased uptake of TEA, whereas TEA efflux from OCT1- and OCT2-expressing oocytes was not stimulated by inward proton gradient, in consistent with basolateral organic Cation Transport in the kidney. Inhibition of TEA uptake by various organic Cations revealed that apparent substrate spectrum of OCT2 was similar with that of OCT1. However, the affinity of procainamide to OCT1 was higher than that to OCT2. Uptake of 1-methyl-4-phenylpyridinium was stimulated by OCT2 as well as OCT1, but uptake of levofloxacin, a zwitterion, was not stimulated by both OCTs. These results suggest that OCT2 is a multispecific organic Cation Transporter with the characteristics comparable to those of the basolateral organic Cation Transporter in the kidney.
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Cholesterol modulates organic Cation Transport activity and lipid fluidity in rat renal brush-border membranes
Biochimica et Biophysica Acta, 1996Co-Authors: Tomohiro Nabekura, Mikihisa Takano, Kenichi InuiAbstract:The role of cholesterol in organic Cation Transport was studied in rat renal brush-border membranes. H+ gradient-dependent uptake of the organic Cation tetraethylammonium in brush-border membrane vesicles was stimulated by cholesterol enrichment in a dose-dependent manner. The dissipation rate of the H+ gradient, a driving force for organic Cation Transport in brush-border membranes, was reduced by cholesterol enrichment. Tetraethylammonium uptake in the absence of H+ gradient was also stimulated by cholesterol enrichment. These findings indicate that cholesterol modulates tetraethylammonium uptake by affecting the intrinsic activity of the organic Cation Transporter and the H+ gradient dissipation rate. Therefore, cholesterol content should be an important determinant for organic Cation Transport in renal brush-border membranes.
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Developmental Maturation of Organic Cation Transport in Rat Renal Brush‐border Membranes
Pharmacy and Pharmacology Communications, 1996Co-Authors: Tomohiro Nabekura, Mikihisa Takano, Kenichi InuiAbstract:Organic Cations are actively Transported in the renal brush-border membrane (BBM) by the H+/organic Cation antiport system. In the present study, we investigated the developmental changes in organic Cation Transport in BBM. Uptake of organic Cation tetraethylammonium (TEA) by BBM vesicles from 14-day-old rats was actively driven by the outward H+ gradient and showed apparent overshoot. However, the initial rate and magnitude of the overshoot of TEA uptake by BBM vesicles from 14-day-old rats were smaller than by those from adult (8-week-old) rats. The Transport activity increased with age, and reached the adult level in 28-day-old rats. The dissipation rate of the H+ gradient, a driving force for the organic Cation Transport in BBM, was not increased in 14-day-old rats. H+ gradient-independent TEA-TEA exchange in BBM was also smaller in 14-day-old rats than in adult rats. On the other hand, the substrate specificity of organic Cation Transport system and the affinity of each substrate were identical in the BBM from adult and 14-day-old rats. The H+/organic Cation antiport system, which has characteristics similar to that in adult rats but with low activity, exists in the renal BBM of 14-day-old rats and the Transporter activity matures during postnatal development.
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Modulation of Organic Cation Transport and Lipid Fluidity by Benzyl Alcohol in Rat Renal Brush-border Membranes
Pharmaceutical Research, 1996Co-Authors: Tomohiro Nabekura, Masato Yasuhara, Mikihisa Takano, Michio Kimura, Kenichi InuiAbstract: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.
Kathleen M. Giacomini - One of the best experts on this subject based on the ideXlab platform.
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Expression of human polyspecific renal organic Cation Transport activity in Xenopus laevis oocytes.
Journal of pharmaceutical sciences, 1997Co-Authors: Joanne K. Chun, Micheline Piquette-miller, Lei Zhang, Kathleen M. GiacominiAbstract:Polyspecific organic Cation Transporters in the basolateral and brush border membrane of the kidney play a role in the elimination of many clinically important drugs and endogenous compounds. In this study we report the functional expression of organic Cation Transport activity in Xenopus laevis oocytes injected with poly(A)+RNA (mRNA) isolated from human kidney. Uptake of [14C]tetraethylammonium (TEA) was measured in mRNA-injected or water-injected oocytes, 4 days after injection. In oocytes injected with 50 ng of mRNA isolated from human renal cortex, the uptake of [14C]TEA was significantly increased in comparison with water-injected oocytes (7.2 ± 0.6 and 3.5 ± 0.3 pmol/ oocyte/h, respectively). Injection of 20 ng of an enriched size-fraction (fraction C) of mRNA (mean size of 2.3 kb) resulted in further enhancement of [14C]TEA uptake: [14C]TEA uptake was enhanced six-to seven-fold in oocytes injected with fraction C (23.7 ± 3.7 pmol/oocyte/ h) in comparison with water-injected oocytes. The uptake of TEA in mRNA-injected oocytes was significantly inhibited by 5 mM of unlabeled TEA, cimetidine, and N1-methylnicotinamide. These data suggest that polyspecific organic Cation Transport activity can be successfully expressed in Xenopus laevis oocytes injected with mRNA isolated from human kidney.
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Organic Cation Transport in human renal brush-border membrane vesicles.
American Journal of Physiology-renal Physiology, 1991Co-Authors: G Yuan, Kathleen M. GiacominiAbstract:The renal proximal tubule is responsible for the active elimination of organic Cations. Studies in brush-border membrane vesicles (BBMV) suggest that active organic Cation Transport is mediated by an organic Cation-proton antiporter. The goals of this study were to determine whether this Transporter is expressed in human kidney and to elucidate its characteristics. Transport of the organic Cations N1-[3H]methylnicotinamide (NMN) and [14C]tetraethylammonium (TEA) was determined by rapid filtration in BBMV of donor human kidneys. The uptake of NMN and TEA was driven against a concentration gradient by an outwardly directed proton gradient. NMN uptake was inhibited by the organic Cations TEA, NMN, quinine, and cimetidine, but was not affected by p-aminohippuric acid, cephalexin, and polyamines. The electroneutral Transport of NMN was characterized by a Km of 0.44 +/- 0.07 mM and a Vmax of 24.4 +/- 15.2 pmol.mg protein-1.s-1. The rate of proton efflux from BBMV increased in the presence of an inwardly directe...
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Organic Cation Transport in human renal brush-border membrane vesicles.
American Journal of Physiology-renal Physiology, 1991Co-Authors: G Yuan, Kathleen M. GiacominiAbstract:The renal proximal tubule is responsible for the active elimination of organic Cations. Studies in brush-border membrane vesicles (BBMV) suggest that active organic Cation Transport is mediated by an organic Cation-proton antiporter. The goals of this study were to determine whether this Transporter is expressed in human kidney and to elucidate its characteristics. Transport of the organic Cations N1-[3H]methylnicotinamide (NMN) and [14C]tetraethylammonium (TEA) was determined by rapid filtration in BBMV of donor human kidneys. The uptake of NMN and TEA was driven against a concentration gradient by an outwardly directed proton gradient. NMN uptake was inhibited by the organic Cations TEA, NMN, quinine, and cimetidine, but was not affected by p-aminohippuric acid, cephalexin, and polyamines. The electroneutral Transport of NMN was characterized by a Km of 0.44 +/- 0.07 mM and a Vmax of 24.4 +/- 15.2 pmol.mg protein-1.s-1. The rate of proton efflux from BBMV increased in the presence of an inwardly directe...
Tomohiro Nabekura - One of the best experts on this subject based on the ideXlab platform.
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Cholesterol modulates organic Cation Transport activity and lipid fluidity in rat renal brush-border membranes
Biochimica et Biophysica Acta, 1996Co-Authors: Tomohiro Nabekura, Mikihisa Takano, Kenichi InuiAbstract:The role of cholesterol in organic Cation Transport was studied in rat renal brush-border membranes. H+ gradient-dependent uptake of the organic Cation tetraethylammonium in brush-border membrane vesicles was stimulated by cholesterol enrichment in a dose-dependent manner. The dissipation rate of the H+ gradient, a driving force for organic Cation Transport in brush-border membranes, was reduced by cholesterol enrichment. Tetraethylammonium uptake in the absence of H+ gradient was also stimulated by cholesterol enrichment. These findings indicate that cholesterol modulates tetraethylammonium uptake by affecting the intrinsic activity of the organic Cation Transporter and the H+ gradient dissipation rate. Therefore, cholesterol content should be an important determinant for organic Cation Transport in renal brush-border membranes.
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Developmental Maturation of Organic Cation Transport in Rat Renal Brush‐border Membranes
Pharmacy and Pharmacology Communications, 1996Co-Authors: Tomohiro Nabekura, Mikihisa Takano, Kenichi InuiAbstract:Organic Cations are actively Transported in the renal brush-border membrane (BBM) by the H+/organic Cation antiport system. In the present study, we investigated the developmental changes in organic Cation Transport in BBM. Uptake of organic Cation tetraethylammonium (TEA) by BBM vesicles from 14-day-old rats was actively driven by the outward H+ gradient and showed apparent overshoot. However, the initial rate and magnitude of the overshoot of TEA uptake by BBM vesicles from 14-day-old rats were smaller than by those from adult (8-week-old) rats. The Transport activity increased with age, and reached the adult level in 28-day-old rats. The dissipation rate of the H+ gradient, a driving force for the organic Cation Transport in BBM, was not increased in 14-day-old rats. H+ gradient-independent TEA-TEA exchange in BBM was also smaller in 14-day-old rats than in adult rats. On the other hand, the substrate specificity of organic Cation Transport system and the affinity of each substrate were identical in the BBM from adult and 14-day-old rats. The H+/organic Cation antiport system, which has characteristics similar to that in adult rats but with low activity, exists in the renal BBM of 14-day-old rats and the Transporter activity matures during postnatal development.
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Modulation of Organic Cation Transport and Lipid Fluidity by Benzyl Alcohol in Rat Renal Brush-border Membranes
Pharmaceutical Research, 1996Co-Authors: Tomohiro Nabekura, Masato Yasuhara, Mikihisa Takano, Michio Kimura, Kenichi InuiAbstract: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.
Mikihisa Takano - One of the best experts on this subject based on the ideXlab platform.
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Cholesterol modulates organic Cation Transport activity and lipid fluidity in rat renal brush-border membranes
Biochimica et Biophysica Acta, 1996Co-Authors: Tomohiro Nabekura, Mikihisa Takano, Kenichi InuiAbstract:The role of cholesterol in organic Cation Transport was studied in rat renal brush-border membranes. H+ gradient-dependent uptake of the organic Cation tetraethylammonium in brush-border membrane vesicles was stimulated by cholesterol enrichment in a dose-dependent manner. The dissipation rate of the H+ gradient, a driving force for organic Cation Transport in brush-border membranes, was reduced by cholesterol enrichment. Tetraethylammonium uptake in the absence of H+ gradient was also stimulated by cholesterol enrichment. These findings indicate that cholesterol modulates tetraethylammonium uptake by affecting the intrinsic activity of the organic Cation Transporter and the H+ gradient dissipation rate. Therefore, cholesterol content should be an important determinant for organic Cation Transport in renal brush-border membranes.
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Developmental Maturation of Organic Cation Transport in Rat Renal Brush‐border Membranes
Pharmacy and Pharmacology Communications, 1996Co-Authors: Tomohiro Nabekura, Mikihisa Takano, Kenichi InuiAbstract:Organic Cations are actively Transported in the renal brush-border membrane (BBM) by the H+/organic Cation antiport system. In the present study, we investigated the developmental changes in organic Cation Transport in BBM. Uptake of organic Cation tetraethylammonium (TEA) by BBM vesicles from 14-day-old rats was actively driven by the outward H+ gradient and showed apparent overshoot. However, the initial rate and magnitude of the overshoot of TEA uptake by BBM vesicles from 14-day-old rats were smaller than by those from adult (8-week-old) rats. The Transport activity increased with age, and reached the adult level in 28-day-old rats. The dissipation rate of the H+ gradient, a driving force for the organic Cation Transport in BBM, was not increased in 14-day-old rats. H+ gradient-independent TEA-TEA exchange in BBM was also smaller in 14-day-old rats than in adult rats. On the other hand, the substrate specificity of organic Cation Transport system and the affinity of each substrate were identical in the BBM from adult and 14-day-old rats. The H+/organic Cation antiport system, which has characteristics similar to that in adult rats but with low activity, exists in the renal BBM of 14-day-old rats and the Transporter activity matures during postnatal development.
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Modulation of Organic Cation Transport and Lipid Fluidity by Benzyl Alcohol in Rat Renal Brush-border Membranes
Pharmaceutical Research, 1996Co-Authors: Tomohiro Nabekura, Masato Yasuhara, Mikihisa Takano, Michio Kimura, Kenichi InuiAbstract: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.
Stephen H. Wright - One of the best experts on this subject based on the ideXlab platform.
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Peritubular organic Cation Transport in isolated rabbit proximal tubules
American Journal of Physiology-renal Physiology, 1994Co-Authors: Carlotta E. Groves, Kristen K. Evans, William H. Dantzler, Stephen H. WrightAbstract:The physiological characteristics of peritubular organic Cation Transport were examined by measuring the Transport of the organic Cation tetraethylammonium (TEA) in rabbit renal proximal tubule suspensions and isolated nonperfused rabbit renal proximal tubules. Peritubular organic Cation Transport in both single S2 segments and suspensions of isolated renal proximal tubules was found to be a high-capacity, high-affinity, carrier-mediated process. For tubule suspensions, the maximal capacity of the carrier for TEA (Jmax) and the concentration of TEA at 1/2 Jmax (Kt) (1.49 +/- 0.21 nmol.min-1.mg dry wt-1 and 131 +/- 16 microM, respectively), did not differ significantly from those measured in single S2 segments (Jmax, 1.16 +/- 0.075 nmol.min-1.mg dry wt-1; Kt, 108 +/- 10 microM). In addition, the pattern of inhibition of peritubular TEA Transport by long-chain n-tetraalkylammonium compounds (n = 1-5) was both qualitatively and quantitatively similar in single S2 segments and tubule suspensions, exhibiting a...
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Peritubular organic Cation Transport in isolated rabbit proximal tubules
American Journal of Physiology-Renal Physiology, 1994Co-Authors: Carlotta E. Groves, Kristen K. Evans, William H. Dantzler, Stephen H. WrightAbstract:The physiological characteristics of peritubular organic Cation Transport were examined by measuring the Transport of the organic Cation tetraethylammonium (TEA) in rabbit renal proximal tubule suspensions and isolated nonperfused rabbit renal proximal tubules. Peritubular organic Cation Transport in both single S2 segments and suspensions of isolated renal proximal tubules was found to be a high-capacity, high-affinity, carrier-mediated process. For tubule suspensions, the maximal capacity of the carrier for TEA (Jmax) and the concentration of TEA at 1/2 Jmax (Kt) (1.49 +/- 0.21 nmol.min-1.mg dry wt-1 and 131 +/- 16 microM, respectively), did not differ significantly from those measured in single S2 segments (Jmax, 1.16 +/- 0.075 nmol.min-1.mg dry wt-1; Kt, 108 +/- 10 microM). In addition, the pattern of inhibition of peritubular TEA Transport by long-chain n-tetraalkylammonium compounds (n = 1-5) was both qualitatively and quantitatively similar in single S2 segments and tubule suspensions, exhibiting an increase in inhibitory potency with increasing alkyl chain length. For example, in tubule suspensions, apparent Michaelis constants for inhibition of TEA uptake ranged from 1.3 mM for tetramethylammonium (TMA) to 0.8 microM for tetrapentylammonium (TPeA). To determine whether these compounds were substrates for the peritubular organic Cation Transporter, their effect on the efflux of [14C]TEA from tubule suspensions was examined. A concentration of 0.5 mM of the short-chain tetraalkyls TMA or TEA increased the efflux of [14C]TEA (i.e., trans-stimulated) from tubules in suspension. The longer-chain tetraalkyls tetrapropylammonium, tetrabutylammonium, and TPeA all decreased the efflux of [14C]TEA from tubules in suspension; TPeA completely blocked efflux.(ABSTRACT TRUNCATED AT 250 WORDS)