1,720,985 research outputs found
Functional differences in steroid sulfate uptake of organic anion transporter 4 (OAT4) and organic anion transporting polypeptide 2B1 (OATP2B1) in human placenta
No full textHuman trophoblasts depend on the supply of external precursors such as dehydroepiandrosterone-3-sulfate (DHEA-S) and 16 alpha-OH-DHEA-S for synthesis of estrogens. Recently, we have characterized the uptake of DHEA-S by isolated mononucleated trophoblasts and identified different transporter polypeptides involved in this process. Immunohistochemistry of 1st and 3rd trimester placenta detected organic anion transporter4 (OAT4) and organic anion transporting polypeptide 2B1 (OATP2B1, former name OATP-B) in cytotrophoblast membranes and at the basal surface of the syncytiotrophoblast, indicating that both transporter polypeptides are involved in placental uptake of foetal derived steroid sulfates. In the present study we have characterized and compared the kinetics of DHEA-S and estrone sulfate (E1S) uptake by these transporters stably expressed in FlpIn (TM)-HEK293 cells using the Flp recombinase-mediated site-specific recombination. Uptake of EIS by OAT4- and OATP2B1-transfected cells was highly increased compared to the non-transfected cells. In contrast, DHEA-S uptake was only highly increased in OAT4 (40 times), but only weakly enhanced in OATP2B1 cells. The uptake of DHEA-S and E, S by OAT4 was partly Na+-dependent (about 50%), whereas uptake of DHEA-S by OATP2B1 was Na+-independent. Kinetic analysis of the initial uptake rates of El S by OAT4 and OATP2B1 gave very similar values for K-m (about 20 mu M) and V-max (about 600 pmol/(min x mg protein)). In contrast, the affinity of DHEA-S towards OATP2B1 was about 10 times lower (Km > 200 mu M) then for OAT4 (K-m = 29 mu M). Our results suggest different physiological roles of the two transporter polypeptides in placental uptake of foetal derived steroid sulfates. OATP2B1 seems not to be involved in de novo synthesis of placental estrogens but may contribute to the clearance of estrogen sulfates from foetal circulation. (C) 2008 Elsevier Ltd. All rights reserved
Identification of a human organic anion transporter (hORCTL3, SLC22A13) facilitating urate and high affinity nicotinate exchange in kidney and intestine
No full textHuman renal organic anion transporter 4 operates as an asymmetric urate transporter
No full textHuman organic anion transporter 4 (hOAT4) is located at the apical membrane of proximal tubule cells and involved in renal secretion and reabsorption of endogenous substances as well as many drugs and xenobiotics. This study reevaluated the physiologic role, transport mode, and driving forces of hOAT4. 6-Carboxyfluorescein (6-CF) uptake into HEK293 cells that stably expressed hOAT4 was saturable, resulting in a K-m of 108 mu M. 6-CF as well as [H-3]estrone sulfate ([H-3]ES) accumulation by HEK293-hOAT4 cells were abolished by ES, dehydroepiandrosterone sulfate, sulfinpyrazone, benzbromarone, and probenecid, whereas several OA, including p-aminohippurate (PAH), lactate, pyrazinoate, nicotinate, glutarate, and the diuretic hydrochlorothiazide (HCTZ) exhibited a slight or a NS inhibitory effect. PAH and glutarate are not taken up by HEK293-hOAT4 cells, but they trans-stimulated 6-CF and [H-3]ES uptake, indicating an asymmetric interaction of hOAT4 with these substrates. In chloride-free medium, HEK293-hOAT4-mediated [H-3]PAH efflux was almost abolished, whereas addition of ES restored it comparable to Ringer solution, consistent with a physiologic ES/PAH or PAH/Cl- exchange mode of hOAT4. Moreover, an acidification of the uptake medium increased 6-CF as well as [H-3]ES uptake, which was reduced by nigericin, suggesting that hOAT4 also can operate as an OA/OH- exchanger. hOAT4 facilitates substantial uptake of [C-14]urate, which was elevated 2.6-fold by intracellular HCTZ. Thus, hOAT4 is the long-postulated, low-affinity apical urate anion exchanger that facilitates HCTZ-associated hyperuricemia
Mutation of amino acid 475 of rat organic cation transporter 2 (rOCT2) impairs organic cation transport
No full textOrganic anion transporter 3 (OAT3) and renal transport of the metal chelator 2,3-dimercapto-1-propanesulfonic acid (DMPS)
No full textRecent investigations involving intact rabbit renal proximal tubules indicated that organic anion transporter 3 (OAT3) may be involved in the transport of 2,3-dimercapto-1-propanesulfonic acid (DMPS). Therefore, we evaluated the interaction of OAT3 with DMPS to determine the effect of OAT3 on basolateral DMPS uptake. We used stably transfected HEK293 cells expressing human and rabbit orthologs of the exchanger OAT1 and OAT3. Using 6-carboxyfluorescein (6-CF) as a substrate, the IC(50) determinations for reduced DMPS (DMPSH) revealed a stronger interaction with OAT1 than with OAT3 (rbOAT1, 123.3 +/- 13.7: hOAT1, 85.1 +/- 8.8; rbOAT3, 171.7 +/- 22.3: and hOAT3, 172.2 +/- 36.4 mu mol/L). However, inhibition of 6-CF uptake by the oxidized form of DMPS (DMPSS), the main form of DMPS in the blood, showed a greater affinity for OAT3 (rbOAT1, 237.4 +/- 23; hOAT1, 104.6 +/- 13.1: rbOAT3, 52.4 +/- 7.6: and hOAT3, 31.6 +/- 6.6 mu mol/L). To determine whether DMPSH and DMPSS are substrates for OAT3, we performed efflux studies with [(14)C]glutarate and inwardly directed gradients of glutarate. The inhibitors trans-stimulated the efflux of [(14)C]glutarate, suggesting that OAT3 may be able to transport both forms of DMPS. On the basis of the substantial interaction of OAT3 with DMPSS, we conclude that OAT3 represents the dominant basolateral player in renal detoxification processes resulting from use of DMPS.NIH [DK074022
Gender differences in kidney function
No full textSex hormones influence the development of female (F) and male (M) specific traits and primarily affect the structure and function of gender-specific organs. Recent studies also indicated their important roles in regulating structure and/or function of nearly every tissue and organ in the mammalian body, including the kidneys, causing gender differences in a variety of characteristics. Clinical observations in humans and studies in experimental animals in vivo and in models in vitro have shown that renal structure and functions under various physiological, pharmacological, and toxicological conditions are different in M and F, and that these differences may be related to the sex-hormone-regulated expression and action of transporters in the apical and basolateral membrane of nephron epithelial cells. In this review we have collected published data on gender differences in renal functions, transporters and other related parameters, and present our own microarray data on messenger RNA expression for various transporters in the kidney cortex of M and F rats. With these data we would like to emphasize the importance of sex hormones in regulation of a variety of renal transport functions and to initiate further studies of gender-related differences in kidney structure and functions, which would enable us to better understand occurrence and development of various renal diseases, pharmacotherapy, and drug-induced nephrotoxicity in humans and animals
Interaction of human Organic Anion Transporters with the loop diuretic torasemide and the impact on renal urate excretion
No full textRenal expression of organic anion transporter OAT2 in rats and mice is regulated by sex hormones
No full textThe renal reabsorption and/or excretion of various organic anions is mediated by specific organic anion transporters (OATs). OAT2 (Slc22a7) has been identified in rat kidney, where its mRNA expression exhibits gender differences [females (F) > males (M)]. The exact localization of OAT2 protein in the mammalian kidney has not been reported. Here we studied the expression of OAT2 mRNA by RT-PCR and its protein by Western blotting (WB) and immunocytochemistry (IC) in kidneys of adult intact and gonadectomized M and F, sex hormone-treated castrated M, and prepubertal M and F rats, and the protein in adult M and F mice. In adult rats, the expression of OAT2 mRNA was predominant in the outer stripe (OS) tissue, exhibiting 1) gender dependency (F > M), 2) upregulation by castration and downregulation by ovariectomy, and 3) strong downregulation by testosterone and weak upregulation by estradiol and progesterone treatment. A polyclonal antibody against rat OAT2 on WB of isolated renal membranes labeled a similar to 66-kDa protein band that was stronger in F. By IC, the antibody exclusively stained brush border (BB) of the proximal tubule S3 segment (S3) in the OS and medullary rays (F > M). In variously treated rats, the pattern of 66-kDa band density in the OS membranes and the staining intensity of BB in S3 matched the mRNA expression. The expression of OAT2 protein in prepubertal rats was low and gender independent. In mice, the expression pattern largely resembled that in rats. Therefore, OAT2 in rat (and mouse) kidney is localized to the BB of S3, exhibiting gender differences (F > M) that appear in puberty and are caused by strong androgen inhibition and weak estrogen and progesterone stimulation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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