Uptake Of Paraquat Research Articles

Acid-base treatment of lightweight expanded clay aggregate (LECA) for removal of paraquat from aqueous media

This study focuses on the modification of lightweight expanded clay aggregate (LECA) with sulfuric acid, potassium hydroxide, and sulfuric acid-potassium hydroxide to enhance the removal efficiency of the highly hazardous herbicide (paraquat) from the aqueous solution. The modification results showed that samples activated with sulfuric acid before KOH yielded higher removal efficiency (70.8%) than those activated with acid or base (25.6% and 35.8%, respectively). The paraquat uptake mechanism by LECA was investigated using XRD, XRF, FTIR, FESEM, BET, and zeta potential measurements. Batch adsorption tests were conducted under different conditions using LECA and acid-base-modified LECA. The results indicated the maximum removal efficiency for PQ at 240 min contact time, adsorbent dose of 3.5 g L−1, and pH 9 was achieved with the acid-base treated sample. Experimental data were evaluated with different isothermal, thermodynamic, and kinetic models. The pseudo-second-order model with a correlation coefficient of R2 > 0.99 was congruent with experimental results for LECA and acid-base-activated LECA through kinetic investigations. The highest adsorption capacities for the LECA and acid-base-activated LECA samples, respectively, were 6.12 mg g−1 and 21.23 mg g−1 according to the Langmuir equilibrium isotherm, which offered greater agreement with the experimental results. A negative standard enthalpy change (−21.09 kJ mol−1) and Gibbs free energy change for PQ uptake at 15, 25, and 35 °C indicated an exothermic and spontaneous process. Reusability studies confirmed that the treated adsorbent could successfully remove paraquat even after four regeneration cycles.

Anthrahydroquinone-2-6-disulfonate is a novel, powerful antidote for paraquat poisoning

Paraquat (PQ) is a widely used fast-acting pyridine herbicide. Accidental ingestion or self-administration via various routes can cause severe organ damage. Currently, no effective antidote is available commercially, and the mortality rate of poisoned patients is exceptionally high. Here, the efficacy of anthrahydroquinone-2-6-disulfonate (AH2QDS) was observed in treating PQ poisoning by constructing in vivo and ex vivo models. We then explored the detoxification mechanism of AH2QDS. We demonstrated that, in a rat model, the PQ concentration in the PQ + AH2QDS group significantly decreased compared to the PQ only group. Additionally, AH2QDS protected the mitochondria of rats and A549 cells and decreased oxidative stress damage, thus improving animal survival and cell viability. Finally, the differentially expressed genes were analysed in the PQ + AH2QDS group and the PQ group by NextGen sequencing, and we verified that Nrf2’s expression in the PQ + AH2QDS group was significantly higher than that in the PQ group. Our work identified that AH2QDS can detoxify PQ by reducing PQ uptake and protecting mitochondria while enhancing the body's antioxidant activity.

Cellular uptake of paraquat determines subsequent toxicity including mitochondrial damage in lung epithelial cells.

Paraquat (PQ) is one of the commonly used herbicides in the world, despite its high toxicity. The ingestion of PQ accidentally or intentionally causes severe damage in diverse organs including the lung. Pulmonary fibrosis triggered by PQ accumulation in the lung epithelial cells is one of the major causes of death. This study investigated the intracellular accumulation of PQ, reactive oxygen species (ROS) generation and mitochondrial injury using two lung epithelial cell lines A549 and BEAS-2B (BEAS). Although A549 exhibit greater resistance to oxidative stress than BEAS, a cytotoxicity assay for PQ demonstrated that EC50 for lethality in A549 was 7 times lower than that in BEAS. When exposed to PQ at a concentration around EC50 for lethality, the amount of ROS generated in A549 was as low as that in BEAS. Conversely, the cellular concentration of PQ in A549 after exposure was higher than that in BEAS, which suggests a distinct difference in the susceptibility to PQ between these cell lines. After a 16 h exposure to PQ, mitochondrial membrane potential (MMP) decreased in A549, but decreased only slightly in BEAS even following a 30 h exposure. PQ-exposed A549 reduced an accumulation of PTEN-induced kinase 1 (PINK1), which works in degradation of damaged mitochondria, following the decrease of MMP, whereas PQ did not decline the PINK1 in BEAS. These results suggest that mitochondrial dysfunction due to cellular accumulation of PQ might contribute to the PQ-provoked toxicity more than the ROS generation in the lung epithelial cells.

Magnetic Hybrid Nanosorbents for the Uptake of Paraquat from Water.

Although paraquat has been banned in European countries, this herbicide is still used all over the world, thanks to its low-cost, high-efficiency, and fast action. Because paraquat is highly toxic to humans and animals, there is interest in mitigating the consequences of its use, namely by implementing removal procedures capable of curbing its environmental and health risks. This research describes new magnetic nanosorbents composed of magnetite cores functionalized with bio-hybrid siliceous shells, that can be used to uptake paraquat from water using magnetically-assisted procedures. The biopolymers κ-carrageenan and starch were introduced into the siliceous shells, resulting in two hybrid materials, Fe3O4@SiO2/SiCRG and Fe3O4@SiO2/SiStarch, respectively, that exhibit a distinct surface chemistry. The Fe3O4@SiO2/SiCRG biosorbents displayed a superior paraquat removal performance, with a good fitting to the Langmuir and Toth isotherm models. The maximum adsorption capacity of paraquat for Fe3O4@SiO2/SiCRG biosorbents was 257 mg·g−1, which places this sorbent among the best systems for the removal of this herbicide from water. The interesting performance of the κ-carrageenan hybrid, along with its magnetic properties and good regeneration capacity, presents a very efficient way for the remediation of water contaminated with paraquat.

Clathrin-Dependent Uptake of Paraquat into SH-SY5Y Cells and Its Internalization into Different Subcellular Compartments.

The herbicide paraquat (PQ) is an exogenous toxin that allows the selective activation of dopaminergic neurons in the mesencephalon to induce injury and also causes its apoptosis in vitro. However, uptake mechanisms between PQ and neurons remain elusive. To address this issue, we undertook a study of PQ endocytosis in a dopaminergic SH-SY5Y cell line as well as explored the subsequent subcellular location and potential functional analysis of PQ. The PQ was found to bind the SH-SY5Y cell membrane and then became internalized via a clathrin-dependent pathway. PQ was internalized by many subcellular organelles in a time- and dose-dependent manner. Interestingly, the taken up PQ and secretogranin III (SCG3), which became dysregulated with PQ treatment that induced SH-SY5Y apoptosis in our previous study, colocalized in cytoplasmic vesicles. Taken together, our findings indicate that PQ is endocytosed by SH-SY5Y cells and that its multiple, subcellular localizations indicate PQ may potentially be involved in subcellular-level functions. More importantly, PQ distributing preferentially into SCG3-positive vesicles demonstrates its selective targeting which may affect SCG3 and cargoes carried by SCG3-positive vesicles. Therefore, it is reasonable to infer that PQ toxic insults may potentially interfere with neurotransmitter storage and transport associated with secretory granules.

Pepper and Tomato Root Uptake of Paraquat and Flumioxazin

Fresh market pepper and tomato are important crops in Florida. Production primarily occurs on raised beds covered with plastic mulch. Weeds emerging between the rows are often controlled with multiple applications of burndown and soil-residual herbicides. Crop damage attributed to root uptake of herbicides applied between the rows has been reported. An experiment was conducted in a greenhouse at the Gulf Coast Research and Education Center to examine the effect of root uptake of paraquat and paraquat tank-mixed with flumioxazin on pepper and tomato growth and yield. Herbicides were applied via subsurface irrigation at 0.0625×, 0.125×, 0.25×, 0.5×, 1×, 2×, 4×, 8×, and 16× labeled rates. The 1× rate was based on the estimated label rate that would be applied per plant in the field and was 0.122 g ai plant−1(1,542 g ai ha−1) and 0.011 g ai plant−1(143 g ai ha−1) for paraquat and flumioxazin, respectively. Root uptake caused necrosis of the veins, followed by complete tissue death at higher rates. The percentage of crop damage increased with herbicide rate for both species (P < 0.0001), with greater damage observed at the lower rates with the tank mix than with the paraquat alone. A reduction in shoot biomass and fruit yield of both crops was observed following root uptake. These results suggest that uptake of paraquat or paraquat tank-mixed with flumioxazin by pepper and tomato roots in a field situation is possible.

Several transport systems contribute to the intestinal uptake of Paraquat, modulating its cytotoxic effects

Paraquat (PQ) is an extremely toxic herbicide upon oral ingestion that lacks a specific antidote. In case of intoxication, treatment primarily relies on limiting its intestinal absorption. In this study, we elucidate the intestinal transport mechanisms of PQ uptake using Caco-2 cells as a model of the human intestinal epithelium. The cells were incubated with a wide range of PQ concentrations (0–5000μM) for 24h with or without simultaneous exposure to different transporters substrates/inhibitors including, choline or hemicolinium-3 (for choline carrier-mediated transport system inhibition) and putrescine, trifluoperazine, valine, lysine, arginine or N-ethylmaleimide (for basic amino acid transport systems inhibition). PQ cytotoxicity was evaluated by the MTT reduction assay and correlated with PQ intracellular levels quantified by gas chromatography-ion trap-mass spectrometry (GC–IT/MS). Potential interactions of PQ with the substrates/inhibitors of the transport systems were investigated and discarded by infrared spectroscopy.Our results showed a significant reduction in PQ intracellular accumulation and, consequently, in PQ cytotoxicity, in the presence of both choline and hemicolinium-3, demonstrating that the choline carrier-mediated transport system is partially involved in PQ intestinal uptake. Likewise, PQ cytotoxicity and intracellular accumulation were significantly attenuated by simultaneous exposure to putrescine, trifluoperazine, valine, lysine, arginine and N-ethylmaleimide. These data suggested the involvement of more than one of the basic amino acids transport systems, including the y+, b0,+ or y+L systems.In conclusion, this study demonstrated that several transport systems mediate PQ intestinal absorption and, therefore, their modulation may provide alternative efficient pathways for limiting PQ toxicity in intoxication scenarios.

Mechanisms of resistance to paraquat in plants

The aim of this brief review is to draw information from studies of the mechanism of evolved resistance in weeds, together with information from laboratory studies of paraquat tolerance in model plants. Plants having mutations that limit paraquat uptake into cytoplasm, that confer various stress tolerances or that have transgenes that co-express two or more of the chloroplast Halliwell-Asada cycle enzymes can all exhibit enhanced tolerance to paraquat. However, none of these mechanisms correspond to the high-level resistances that have evolved naturally in weeds. Most, but not all, of the evidence from studies of paraquat-resistant biotypes of weeds can reasonably be reconciled with the proposal of a single major gene mechanism that sequesters paraquat away from chloroplasts and into the vacuole. However, the molecular details of this putative mechanism remain ill-defined.

RBE4 cells are highly resistant to paraquat‐induced cytotoxicity: studies on uptake and efflux mechanisms

Paraquat (PQ) is a widely used, highly toxic and non-selective contact herbicide, which has been associated with central neurotoxic effects, namely the development of Parkinson's disease, but whose effects to the blood-brain barrier (BBB) itself have rarely been studied. This work studied the mechanisms of PQ uptake and efflux in a rat's BBB cell model, the RBE4 cells. PQ is believed to enter cells using the basic or neutral amino acid or polyamine transport systems or through the choline-uptake system. In contrast, PQ efflux from cells is reported to be mediated by P-glycoprotein. Therefore, we evaluated PQ-induced cytotoxicity and the effect of some substrates/blockers of these transporters (such as arginine, L-valine, putrescine, hemicholinium-3 and GF120918) on such cytotoxicity. RBE4 cells were shown to be extremely resistant to PQ after 24 h of exposure; even at concentrations as high as 50 mM approximately 45% of the cells remained viable. Prolonging exposure until 48 h elicited significant cytotoxicity only for PQ concentrations above 5 mM. Although hemicholinium-3, a choline-uptake system inhibitor, significantly protected cells against PQ-induced toxicity, none of the effects were observed for arginine, L-valine or putrescine. Meanwhile, inhibiting the efflux pump P-glycoprotein using GF120918 significantly enhanced PQ-induced cytotoxicity. In conclusion, PQ used the choline-uptake system, instead of the transporters for the basic or neutral amino acids or for the polyamines, to enter RBE4 cells. P-glycoprotein extrudes PQ back to the extracellular medium. However, this efflux mechanism only partially explains the observed RBE4 resistance to PQ.

Paraquat Resistant1, a Golgi-localized putative transporter protein, is involved in intracellular transport of paraquat.

Paraquat is one of the most widely used herbicides worldwide. In green plants, paraquat targets the chloroplast by transferring electrons from photosystem I to molecular oxygen to generate toxic reactive oxygen species, which efficiently induce membrane damage and cell death. A number of paraquat-resistant biotypes of weeds and Arabidopsis (Arabidopsis thaliana) mutants have been identified. The herbicide resistance in Arabidopsis is partly attributed to a reduced uptake of paraquat through plasma membrane-localized transporters. However, the biochemical mechanism of paraquat resistance remains poorly understood. Here, we report the identification and characterization of an Arabidopsis paraquat resistant1 (par1) mutant that shows strong resistance to the herbicide without detectable developmental abnormalities. PAR1 encodes a putative l-type amino acid transporter protein localized to the Golgi apparatus. Compared with the wild-type plants, the par1 mutant plants show similar efficiency of paraquat uptake, suggesting that PAR1 is not directly responsible for the intercellular uptake of paraquat. However, the par1 mutation caused a reduction in the accumulation of paraquat in the chloroplast, suggesting that PAR1 is involved in the intracellular transport of paraquat into the chloroplast. We identified a PAR1-like gene, OsPAR1, in rice (Oryza sativa). Whereas the overexpression of OsPAR1 resulted in hypersensitivity to paraquat, the knockdown of its expression using RNA interference conferred paraquat resistance on the transgenic rice plants. These findings reveal a unique mechanism by which paraquat is actively transported into the chloroplast and also provide a practical approach for genetic manipulations of paraquat resistance in crops.

Doxorubicin decreases paraquat accumulation and toxicity in Caco-2 cells

P-glycoprotein (P-gp) is an efflux pump belonging to the ATP-binding cassette transporter superfamily expressed in several organs. Considering its potential protective effects, the induction of de novo synthesis of P-gp could be used therapeutically in the treatment of intoxications by its substrates. The herbicide paraquat (PQ) is a P-gp substrate responsible for thousands of fatal intoxications worldwide that still lacks an effective antidote.The aim of the present work was to evaluate the effectiveness of such an antidote by testing whether doxorubicin (DOX), a known P-gp inducer, could efficiently protect Caco-2 cells against PQ cytotoxicity, 6h after the incubation with the herbicide, reflecting a real-life intoxication scenario. Cytotoxicity was evaluated by the MTT assay and PQ intracellular concentrations were measured by gas chromatography–ion trap-mass spectrometry (GC–IT-MS). Also, the DOX modulatory effect on choline uptake transport system was assessed by measuring the uptake of [3H]-choline.The results show that DOX exerts protective effects against PQ cytotoxicity, preventing the intracellular accumulation of the herbicide. These protective effects were not completely prevented by the incubation with the UIC2 antibody, a specific P-gp inhibitor, suggesting the involvement of alternative protection mechanisms. In fact, DOX also efficiently inhibited the choline transport system that influences PQ cellular uptake.In conclusion, in this cellular model, DOX effectively protects against PQ toxicity by inducing P-gp and through the interaction with the choline transporter, suggesting that compounds presenting this double feature of promoting the efflux and limiting the uptake of PQ could be used as effective antidotes to treat intoxications.

Natural variation in a polyamine transporter determines paraquat tolerance in Arabidopsis

Polyamines (PAs) are ubiquitous, polycationic compounds that are essential for the growth and survival of all organisms. Although the PA-uptake system plays a key role in mammalian cancer and in plant survival, the underlying molecular mechanisms are not well understood. Here, we identified an Arabidopsis L-type amino acid transporter (LAT) family transporter, named RMV1 (resistant to methyl viologen 1), responsible for uptake of PA and its analog paraquat (PQ). The natural variation in PQ tolerance was determined in 22 Arabidopsis thaliana accessions based on the polymorphic variation of RMV1. An RMV1-GFP fusion protein localized to the plasma membrane in transformed cells. The Arabidopsis rmv1 mutant was highly resistant to PQ because of the reduction of PQ uptake activity. Uptake studies indicated that RMV1 mediates proton gradient-driven PQ transport. RMV1 overexpressing plants were hypersensitive to PA and PQ and showed elevated PA/PQ uptake activity, supporting the notion that PQ enters plant cells via a carrier system that inherently functions in PA transport. Furthermore, we demonstrated that polymorphic variation in RMV1 controls PA/PQ uptake activity. Our identification of a molecular entity for PA/PQ uptake and sensitivity provides an important clue for our understanding of the mechanism and biological significance of PA uptake.

Caveola is a key vehicle for paraquat uptake into lung

Abstract Paraquat dichloride (PQ) is an effective and widely used herbicide for eliminating weeds. However, once being accidentally or voluntarily ingested, PQ-poisoned patients have the very high incidence of adult respiratory distress syndrome because lung can actively absorb PQ. Since the 1970s, evidence suggested that polyamine competitively inhibited uptake of PQ into lung tissue; therefore, polyamine transport system has been regarded as an important vehicle for PQ uptake into lung. However, so far, we cannot clone or detect the polyamine transport system in mammalian animal. Recent evidence from diverse sources has suggested that caveola may be an important vehicle for polyamine absorption into lung. Herein we hypothesise that caveola is a key vehicle for PQ uptake in lung and hence blocking the expression of caveola may serve as new targets for treatment of PQ poisoning.

Loss of AtPDR11, a plasma membrane‐localized ABC transporter, confers paraquat tolerance in Arabidopsis thaliana

Paraquat is one of the most widely used herbicides in the world. However, no paraquat transporter has been isolated in plants. Here, we describe paraquat-tolerant mutant pqt24-1, isolated from an activation-tagging library on the basis of its tolerance to 2 μm paraquat in the seedling stage. Molecular analysis revealed that the T-DNA was inserted in the 13th exon of At1g66950, which encodes AtPDR11, a member of the ATP-binding cassette transporter superfamily. As a result, AtPDR11 was knocked out in the mutant. Loss-of-function mutations of AtPDR11 led to reduced paraquat accumulation in plant cells. In addition, the AtPDR11 protein was specifically localized in the plasmalemma, suggesting AtPDR11 as a potential transporter of paraquat. This conclusion was supported by kinetic analysis of paraquat import. Further studies showed that the transcript level of AtPDR11 could be strongly induced by paraquat and other abiotic stresses including H(2) O(2) , indicating possible up-regulation of AtPDR11 expression by oxidative stress signaling. Thus, our data suggest that paraquat is an opportunistic substrate of AtPDR11 and the enhanced paraquat tolerance of pqt24-1 is due to reduced uptake of paraquat into plant cells.

Assessment of Fetal Brain Uptake of Paraquat In Utero Using In Vivo PET/CT Imaging

Prenatal in utero conditions are thought to play a role in the development of adult diseases including Parkinson's disease (PD). Paraquat is a common herbicide with chemical structure similar to 1-methyl-4-phenyl 1,2,3,6-tetrahydropyridine, a neurotoxin known to induce parkinsonism. In order to assess the role of in utero paraquat exposure in PD, uptake in maternal and fetal brains were measured using positron emission tomography (PET)/computed tomography (CT) imaging. Two anesthetized pregnant rhesus macaques in the late second trimester of pregnancy were given bolus iv injections of ¹¹C-paraquat, and whole-body PET/CT imaging was performed. Using maternal ventricular blood pool as the input function, the unidirectional influx rate constants (K(i)s), a measure of the irreversible transport of paraquat from plasma to brain, were calculated for the maternal and fetal brains using Patlak graphical analysis. Results indicate minimal uptake of paraquat by both maternal and fetal brains with average K(i)s of 0.0009 and 0.0016 per minute, respectively. The highest regional cerebral uptake in the maternal brain (0.0009% injected dose) was seen in the pineal gland, a structure known to lack a blood brain barrier. The finding of minimal paraquat uptake in maternal and fetal brains is similar to previous findings in adult male macaques and extends the contention that a single acute paraquat exposure, prenatally or postnatally, is unlikely to play a role in PD.

Protective Effects of Liposomal N-Acetylcysteine against Paraquat-Induced Cytotoxicity and Gene Expression

Paraquat (PQ) is a herbicide that preferentially accumulates in the lung and exerts its cytotoxicity via the generation of reactive oxygen species (ROS). There is no specific treatment for paraquat poisoning. Attempts have been made to increase the antioxidant status in the lung using antioxidants (e.g., superoxide dismutase, vitamin E, N-acetylcysteine) but the outcome from such treatments is limited. Encapsulation of antioxidants in liposomes improves their therapeutic potential against oxidant-induced lung damage because liposomes facilitate intracellular delivery and prolong the retention of entrapped agents inside the cell. In the present study, we compared the effectiveness of conventional N-acetylcysteine (NAC) and liposomal-NAC (L-NAC) against PQ-induced cytotoxicity and examined the mechanism(s) by which these antioxidant formulations conferred cytoprotection. The effects of NAC or L-NAC against PQ-induced cytotoxicity in A549 cells were assessed by measuring cellular PQ uptake, intracellular glutathione content, ROS levels, mitochondrial membrane potential, cellular gene expression, inflammatory cytokine release and cell viability. Pretreatment of cells with L-NAC was significantly more effective than pretreatment with the conventional drug in reducing PQ-induced cytotoxicity, as indicated by the biomarkers used in this study. Our results suggested that the delivery of NAC as a liposomal formulation improves its effectiveness in counteracting PQ-induced cytotoxicity.

Cytotoxicity and gene array analysis of alveolar epithelial A549 cells exposed to paraquat

Paraquat (PQ), a commonly used herbicide, is highly toxic to humans and animals. The primary injury occurs in the lung, where PQ is actively taken up by alveolar epithelial cells and consequently produces damaging reactive oxygen species (ROS) via redox cycling. ROS have also been shown to induce expression of several early response genes and to activate transcription factors, which may contribute to the inflammatory response associated with PQ injury. In order to further elucidate the mechanism(s) of PQ injury, we investigated its effects on the cellular status and gene expression profile of immortalized human alveolar epithelial A549 cells in vitro. Incubation of cells with PQ resulted in concentration- and time-dependent PQ uptake, which correlated with increases in intracellular ROS levels and decreases in intracellular glutathione content, mitochondrial membrane potential, and cell viability. Gene array analysis showed differential expression in response to PQ exposure over time, particularly increases in: (i) the expression of growth arrest and cell cycle-related genes (e.g. CDKN1A, DDIT3 GADD45A, GDF15, MDM2, EGR1, CASP10, CASP8) and (ii) the expression of pro-inflammatory genes (e.g. IL1A, IL6, IL18, NFKB1, SERPINE1), which correlated with increases in the secretion of pro-inflammatory cytokines (e.g. IL-8, IL-6). These data suggest that uptake of PQ by A549 cells altered the cellular redox status and the expression of several early response genes, including the inflammatory response, all of which might contribute to the overall cytotoxicity of PQ.

Complex I Is the Major Site of Mitochondrial Superoxide Production by Paraquat

Paraquat (1,1'-dimethyl-4,4'-bipyridinium dichloride) is widely used as a redox cycler to stimulate superoxide production in organisms, cells, and mitochondria. This superoxide production causes extensive mitochondrial oxidative damage, however, there is considerable uncertainty over the mitochondrial sites of paraquat reduction and superoxide formation. Here we show that in yeast and mammalian mitochondria, superoxide production by paraquat occurs in the mitochondrial matrix, as inferred from manganese superoxide dismutase-sensitive mitochondrial DNA damage, as well as from superoxide assays in isolated mitochondria, which were unaffected by exogenous superoxide dismutase. This paraquat-induced superoxide production in the mitochondrial matrix required a membrane potential that was essential for paraquat uptake into mitochondria. This uptake was of the paraquat dication, not the radical monocation, and was carrier-mediated. Experiments with disrupted mitochondria showed that once in the matrix paraquat was principally reduced by complex I (mammals) or by NADPH dehydrogenases (yeast) to form the paraquat radical cation that then reacted with oxygen to form superoxide. Together this membrane potential-dependent uptake across the mitochondrial inner membrane and the subsequent rapid reduction to the paraquat radical cation explain the toxicity of paraquat to mitochondria.

Role of transporters in paraquat resistance of horseweed Conyza canadensis (L.) Cronq.

Paraquat (Pq) inducible transporters are presumed to play a role in the resistance mechanism of horseweed and to function by carrying paraquat to a metabolically inactive compartment. The uptake and intracellular localisation of paraquat, the effect of transporter inhibitors on resistance, and paraquat-induced gene expression were studied to obtain a better understanding of the mechanism of resistance. Investigations proved that paraquat entered the cells of both resistant and susceptible biotypes, approached the maximum within the first hour in chloroplasts, and then declined in all organelle fractions. In the resistant biotype paraquat was located in the vacuoles a day after treatment. Selective transporter inhibitors blocked the sequestration of paraquat, suggesting the participation of not directly energized transporters. Four EST fragments were identified that were expressed in response to paraquat. Two of them are thought to play a role in the general stress response (Ferr2, Myb). The others exhibit a similarity to transporters (EmrE, CAT) and could conceivably be involved in the intracellular transport of paraquat and the mechanism of resistance.

Kinetics of paraquat in the isolated rat lung: Influence of sodium depletion

Paraquat accumulates in the lung through a characteristic polyamine uptake system. It has been previously shown that paraquat uptake can be significantly prevented if extracellular sodium (Na+) is reduced, although the available data correspond to experiments performed using tissue slices or incubated cells. This type of in vitro study fails to give information on the actual behaviour occurring in vivo since the anatomy and physiology of the studied tissue is disrupted. Accordingly, the aim of the present study was to explore the usefulness of the isolated rat lung model when applied to characterize the kinetic behaviour of paraquat in this tissue after bolus injection under standard experimental conditions as well as to evaluate the influence of iso-osmotic replacement of Na+ by lithium (Li+) in the perfusion medium. The obtained results show that the present isolated rat lung model is useful for the analysis of paraquat toxicokinetics, which is reported herein for the first time. It was also observed that Na+ depletion in the perfusion medium leads to a decreased uptake of paraquat in the isolated rat lung, although it seems that this condition does not contribute to improve the elimination of paraquat once the herbicide reaches the extravascular structures of the tissue, since the paraquat tissue wash-out phase is similar under both experimental conditions assayed.