Home About us Contact
|
Home About us Contact | ||
|
|
||
Influx Transporters (influx + transporter)
Selected AbstractsTcYSL3, a member of the YSL gene family from the hyper-accumulator Thlaspi caerulescens, encodes a nicotianamine-Ni/Fe transporterTHE PLANT JOURNAL, Issue 1 2007Delphine Gendre Summary The two main features of plant hyper-accumulator species are the massive translocation of heavy metal ions to the aerial parts and their tolerance to such high metal concentrations. Recently, several lines of evidence have indicated a role for nicotianamine (NA) in metal homeostasis, through the chelation and transport of NA,metal complexes. The function of transport of NA,metal chelates, required for the loading and unloading of vessels, has been assigned to the Yellow Stripe 1 (YSL)-Like family of proteins. We have characterized three YSL genes in Thlaspi caerulescens in the context of hyper-accumulation. The three YSL genes are expressed at high rates compared with their Arabidopsis thaliana homologs but with distinct patterns. While TcYSL7 was highly expressed in the flowers, TcYSL5 was more highly expressed in the shoots, and the expression of TcYSL3 was equivalent in all the organs tested. In situ hybridizations have shown that TcYSL7 and TcYSL5 are expressed around the vasculature of the shoots and in the central cylinder in the roots. The exposure to heavy metals (Zn, Cd, Ni) does not affect the high and constitutive expression of the TcYSL genes. Finally, we have demonstrated by mutant yeast complementation and uptake measurements that TcYSL3 is an Fe/Ni,NA influx transporter. This work provides therefore molecular, histological and biochemical evidence supporting a role for YSL transporters in the overall scheme of NA and NA,metal, particularly NA,Ni, circulation in a metal hyper-accumulator plant. [source] Involvement of an influx transporter in the blood,brain barrier transport of naloxoneBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 4 2010Toyofumi Suzuki Abstract Naloxone, a potent and specific opioid antagonist, has been shown in previous studies to have an influx clearance across the rat blood,brain barrier (BBB) two times greater than the efflux clearance. The purpose of the present study was to characterize the influx transport of naloxone across the rat BBB using the brain uptake index (BUI) method. The initial uptake rate of [3H]naloxone exhibited saturability in a concentration-dependent manner (concentration range 0.5,µM to 15,mM) in the presence of unlabeled naloxone. These results indicate that both passive diffusion and a carrier-mediated transport mechanism are operating. The in vivo kinetic parameters were estimated as follows: the Michaelis constant, Kt, was 2.99±0.71,mM; the maximum uptake rate, Jmax, was 0.477±0.083,µmol/min/g brain; and the nonsaturable first-order rate constant, Kd, was 0.160±0.044,ml/min/g brain. The uptake of [3H]naloxone by the rat brain increased as the pH of the injected solution was increased from 5.5 to 8.5 and was strongly inhibited by cationic H1 -antagonists such as pyrilamine and diphenhydramine and cationic drugs such as lidocaine and propranolol. In contrast, the BBB transport of [3H]naloxone was not affected by any typical substrates for organic cation transport systems such as tetraethylammonium, ergothioneine or L -carnitine or substrates for organic anion transport systems such as p -aminohippuric acid, benzylpenicillin or pravastatin. The present results suggest that a pH-dependent and saturable influx transport system that is a selective transporter for cationic H1 -antagonists is involved in the BBB transport of naloxone in the rat. Copyright © 2010 John Wiley & Sons, Ltd. [source] Differential retention of ,-vitamin E is correlated with its transporter gene expression and growth inhibition efficacy in prostate cancer cellsTHE PROSTATE, Issue 5 2007Jing Ni Abstract BACKGROUND Epidemiological studies showed Vit E has protective effects against prostate cancer (PCa). Interestingly, different prostate cancer cells have different sensitivity to ,-Vit E or VES treatment. The goal of this study is to determine whether cellular Vit E bioavailability and its transport proteins are important contributing factors. METHODS ,-Vit E and its ester form, VES, were used to treat prostate cancer LNCaP, PC3, and DU145 cells, and their growth rates were determined by MTT assay. Cellular levels of Vit E were quantified using HPLC as the index of bioavailability. The expression levels of Vit E transport proteins were determined by real-time PCR. RESULTS Among these PCa cells, only LNCaP cells were sensitive to 20 µM ,-Vit E treatment, while both LNCaP and PC3 cells were sensitive to 20 µM VES treatment. Coordinately, cellular levels of ,-Vit E and VES positively correlated to their inhibitory effects. Further study found expression levels of Vit E transport proteins, including tocopherol associated protein (TAP), scavenger receptor class B type I (SR-BI), ,-tocopherol transfer protein (TTP), and ATP binding cassette transporter A1 (ABCA1), were different in various PCa cells, which may contribute to cellular Vit E bioavailability. This notion is further supported by the findings that overexpression or knockdown of TTP could coordinately alter cellular ,-Vit E levels in PCa cells. CONCLUSION Antiproliferative efficacy of ,-Vit E is correlated with its cellular bioavailability in PCa cells. Modulating the expression of the efflux or influx transporters could sensitize the growth inhibition efficacy of Vit E in prostate cancer cells. Prostate 67: 463,471, 2007. © 2007 Wiley-Liss, Inc. [source] Active-Site Concentrations of Chemicals , Are They a Better Predictor of Effect than Plasma/Organ/Tissue Concentrations?BASIC AND CLINICAL PHARMACOLOGY & TOXICOLOGY, Issue 3 2010Margareta Hammarlund-Udenaes In contrast, the total concentrations of the drug in plasma/organ/tissue also include the protein- or tissue-bound molecules that are pharmacologically inactive. Plasma and whole tissue concentrations are used as predictors of effects and side effects because of their ease of sampling, while the concentrations of unbound drug in tissue are more difficult to measure. However, with the introduction of microdialysis and subsequently developed techniques, it has become possible to test the free drug hypothesis. The brain is an interesting organ in this regard because of the presence of the blood-brain barrier with its tight junctions and active efflux and influx transporters. We have proposed that research into brain drug delivery be divided into three main areas: the rate of delivery (PS, CLin), the extent of delivery (Kp,uu) and the non-specific affinity of the drug to brain tissue, described by the volume of distribution of unbound drug in the brain (Vu,brain). In this way, the concentration of unbound drug at the target site can be estimated from the total brain concentration and the plasma concentration after measuring the fraction of unbound drug. Results so far fully support the theory that active site concentrations are the best predictors when active transport is present. However, there is an urgent need to collect more relevant data for predicting active site concentrations in tissues with active transporters in their plasma membranes. [source] Cultured CD4T cells and primary human lymphocytes express hOATPs: intracellular accumulation of saquinavir and lopinavirBRITISH JOURNAL OF PHARMACOLOGY, Issue 6 2008O Janneh Background and purpose: Drug efflux tranporters (P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP)) limit the cellular uptake of human immunodeficiency virus protease inhibitors but the contribution of influx transporters in cells that (over)express P-gp or MRP is less clear. Here, we studied the expression of one influx transporter system, human organic anion-transporting polypeptide (hOATP), in some T-cell lines (CEM, CEMVBL, CEME1000) and in peripheral blood mononuclear cells (PBMCs) and examined the effects of manipulation of influx/efflux transporters on the uptake of saquinavir and lopinavir. Experimental approach: The expression of hOATPs was studied by PCR. We used hOATP substrate or inhibitor (estrone-3-sulphate (E-3-S) or montelukast, respectively) and inhibitors of P-gp (XR9576) and MRP (MK571 and frusemide) to study functional interactions between influx and efflux transporters in the uptake of saquinavir and lopinavir. Lipophilicity of the drugs was measured by octanol/saline partition coefficient. Key results: CEM cells, their variants and PBMCs express various hOATP isoforms, with OATP3A1 detected in all of the cells. MK571, XR9576 and frusemide increased the uptake of saquinavir and lopinavir. E-3-S and montelukast reduced the uptake of saquinavir and lopinavir in some, but not all, of the cells. Pretreatment of the cells with MK571, XR9576 or frusemide, followed by E-3-S co-incubation reduced the cellular accumulation of saquinavir and lopinavir. Lopinavir is much more lipophilic than saquinavir. Conclusions and implications: Human OATPs, MRP, P-gp and lipophilicity determine the cellular uptake and retention of saquinavir and lopinavir. These data may have important implications for drug,drug interactions, drug safety and efficacy. British Journal of Pharmacology (2008) 155, 875,883; doi:10.1038/bjp.2008.320; published online 18 August 2008 [source] | ||||||||||