Short-term Kinetics Research Articles

Experimental evaluation of an efflux–influx model of C exudation by individual apical root segments

The aim of this study was to evaluate if a model describing the efflux and the influx of C through the root surface could be fitted to experimental short-term kinetics of carbon (C) exudation by individual apical root segments in maize (Zea mays L.). The efflux of C was set constant or modelled by a power function of the distance from the apex to simulate the greater release of C around the root tip commonly reported in the literature. The influx was proportional to the C concentration in the external solution to simulate the active re-uptake of exudates by the root. Plants were exposed to full light or to shade to manipulate C allocation to roots. The model with a constant efflux gave satisfactory fits to the kinetics of exudation (average R(2)=0.66). The average gross efflux was then 2.1 mug C cm(-2) root surface h(-1). The model was improved if exudation was set more intense towards the root apex (average R(2)=0.74). The estimated gross efflux decreased then from 5.2 mug C cm(-2) h(-1) at the apex to 1.8 mug C cm(-2) h(-1) for the region located 5-25 cm from the root tip. The decrease in net exudation of individual roots due to the shading of plants was weak, which may indicate that the import of C by the primary roots studied was not reduced significantly. By describing the exudation of an apical root segment of variable length and diameter, the model is a first step in linking exudation to root system architecture models and to whole plant functioning.

Adoptive transfer of syngeneic T cells in HIV‐1 discordant twins indicates rapid regulation of T‐cell homeostasis

The safety and efficacy of adoptive T-cell transfer (ATT) was tested in the context of viral suppression in syngeneic twins discordant for human immunodeficiency virus type 1 (HIV-1) infection. Human leucocyte antigen-matched T cells of seven HIV-negative twins were obtained by lymphapheresis and immediately transfused into the HIV-infected sibling. Four twins received 12 ATTs each, with a mean of 2.10 +/- 0.97 x 10(9) CD4(+) T cells and 1.74 +/- 0.81 x 10(9) CD8(+) T cells. Additional transfers were performed in three more twin pairs to study the short-term kinetics of transfused syngeneic T cells. Mean CD4(+) T-cell counts increased significantly, by 0.133 +/- 0.136 x 10(9) cells/l at 1 h and 0.144 +/- 0.12 x 10(9) cells/l at 3 h post-transfusion (P < 0.0001). Short-term kinetic studies suggested a rapid clearance of transferred T cells from the peripheral blood within minutes due to a distribution to marginal pools. After a mean follow up of 39 months, however, a sustained increase of the mean CD4(+) T-cell count was observed (from 0.232 x 10(9) to 0.523 x 10(9) cells/l) without changes of plasma viraemia. We conclude that ATT combined with highly active antiretroviral therapy is safe and leads to a considerable increase in CD4(+) T-cell numbers. The clearance kinetics of the transfused cells from peripheral blood indicates a very rapid regulation of T-cell homeostasis in HIV infection.

Effect of maximal exercise on the short-term kinetics of zinc metabolism in sedentary men

Objective: To examine the effect of acute exhaustive exercise versus rest on short-term zinc kinetics in men. Design: Crossover design, wherein all subjects were their own control. Setting: University setting,...

Cadmium uptake, translocation and tolerance in the hyperaccumulator Arabidopsis halleri

Arabidopsis halleri is a well-known zinc (Zn) hyperaccumulator, but its status as a cadmium (Cd) hyperaccumulator is less certain. Here, we investigated whether A. halleri can hyperaccumulate Cd and whether Cd is transported via the Zn pathway. Growth and Cd and Zn uptake were determined in hydroponic experiments with different Cd and Zn concentrations. Short-term uptake and root-to-shoot transport were measured with radioactive 109Cd and 65Zn labelling. A. halleri accumulated > 1000 mg Cd kg(-1) in shoot dry weight at external Cd concentrations >or= 5 microm, but the short-term uptake rate of 109Cd was much lower than that of 65Zn. Zinc inhibited short-term 109Cd uptake kinetics and root-to-shoot translocation, as well as long-term Cd accumulation in shoots. Uptake of 109Cd and 65Zn were up-regulated, respectively, by low iron (Fe) or Zn status. A. halleri was much less tolerant to Cd than to Zn. We conclude that A. halleri is able to hyperaccumulate Cd partly, at least, through the Zn pathway, but the mechanisms responsible for cellular Zn tolerance cannot detoxify Cd effectively.

The reactivity of uranyl phosphate mineral phases via microbial weathering: Short vs. long term kinetics

The reactivity of uranyl phosphate mineral phases via microbial weathering: Short vs. long term kinetics

Modelling the leaching of imazapyr in a railway embankment

The use of herbicides on railway tracks is known to present a risk to groundwater, but little is known of the mechanisms influencing leaching through the coarse material used to construct railway embankments. Therefore, in the present study, four different models based on the convection-dispersion equation (CDE) were compared with previously reported field data on the leaching of imazapyr. In particular, the significance of non-equilibrium processes was investigated by comparing different CDE formulations accounting for preferential finger flow, particle-facilitated transport and kinetic sorption. The traditional CDE assuming 'local equilibrium' based on 24 h batch sorption data gave poor results (model efficiency - 1.1). It strongly underestimated leaching of imazapyr in the first 4 months following application, thus confirming the importance of non-equilibrium transport processes. Accounting for short-term sorption kinetics made little difference, giving similar results to the 'local equilibrium' CDE simulation. A simulation accounting for particle-facilitated transport could accurately match this accelerated transport, and also gave the best overall fit to the data (model efficiency 0.76). However, not even this model could match the long-term retention of imazapyr residues observed close to the soil surface more than 1 year after application, and it also underestimated the time of breakthrough to groundwater. This strongly suggests that a long-term retention/sorption process not included in any of the models tested (i.e. sorption hysteresis or bound residues) acted to retard leaching. The formation of 'protected' residues was also indicated by a much slower degradation of imazapyr more than 1 year after application. Industry.

Viral gene transfer combined with bioluminescence imaging (BLI) for longitudinal monitoring of gene expression in targeted brain regions of mice

BLI has emerged as a powerful tool for in vivo analysis of many biological processes. Our goal is to utilize this technology to map spatiotemporal patterns of transcription factor activity in CNS circuits of mice with cardiovascular disease. However, little is known about properties of bioluminescence signals (BLS) in brain, especially in the context of adenoviral (Ad) gene transfer of luciferase (luc). Here we sought to establish the short-term kinetics and long-term stability of the BLS following Ad-mediated delivery of luc to mouse brain. Adult C57 mice underwent intracerebroventricular (ICV) injection (250nl) of Ad encoding the luc gene downstream of either the CMV promoter (3x1010pfu/ml, n=3) or NFκB response elements (1x1011 pfu/ml, n=5). On days 2, 8 and 12 after gene transfer, serial images were taken intermittently over 24 hr following ip injection of luciferin (150 mg/kg) using the Xenogen IVIS® 200. In mice expressing luc in the brain under either promoter, the BLS rose sharply after luciferin administration, peaked at 15 minutes, and decayed 90% by 2 hr, returning to baseline by 24 hr. The peak BLS was robust (eg day 8 AdCMVluc 5.3±.6x105 photons/s) and remained stable out to day 12 (eg 5.6±.5x105 photons/s). Planar spectral analysis revealed a BLS source depth of 1.9±.2mm (n=5) from the skull surface, coinciding with the stereotaxic location of brain nuclei known to be targeted by ICV viral gene delivery. This demonstrates the utility of BLI and establishes optimal parameters for serial monitoring of spatiotemporal patterns of gene expression in targeted brain regions of living mice.

The acute and chronic toxic effects of vitamin A

The acute and chronic effects of vitamin A toxicity are well documented in the literature. Emerging evidence suggests that subtoxicity without clinical signs of toxicity may be a growing concern, because intake from preformed sources of vitamin A often exceeds the recommended dietary allowances (RDA) for adults, especially in developed countries. Osteoporosis and hip fracture are associated with preformed vitamin A intakes that are only twice the current RDA. Assessing vitamin A status in persons with subtoxicity or toxicity is complicated because serum retinol concentrations are nonsensitive indicators in this range of liver vitamin A reserves. The metabolism in well-nourished persons of preformed vitamin A, provided by either liver or supplements, has been studied by several research groups. To control vitamin A deficiency, large therapeutic doses are administered in developing countries to women and children, who often are undernourished. Nevertheless, little attention has been given to the short-term kinetics (ie, after absorption but before storage) of a large dose of vitamin A or to the short- and long-term effects of such a dose given to lactating women on serum and breast-milk concentrations of retinol and its metabolites. Moreover, appropriate dosing regimens have not been systematically evaluated to ascertain the quantitative improvement in vitamin A status of the women and children who receive these supplements. The known acute and chronic effects of vitamin A toxicity have been reported previously. However, further research is needed to ascertain the areas of the world in which subclinical toxicity exists and to evaluate its effects on overall health and well-being.

Bioavailability of Quercetin From Berries and the Diet

: Berries are a rich source of various polyphenols, including the flavonoid quercetin. In this article, the results of three intervention studies investigating the bioavailability of quercetin from berries are reviewed. In the first study, we investigated the short-term kinetics of quercetin after consumption of black currant juice and showed that quercetin is rapidly absorbed from it. In the second study, we showed that plasma quercetin levels increase up to 50% in subjects consuming 100 g/day of bilberries, black currants, and lingonberries as a part of their normal diets for 2 mo. In the third study, healthy subjects consumed a diet high or low in vegetables, berries, and other fruit for 6 wk. Quercetin concentrations nearly doubled in the high-vegetable, -berry, and -other fruit group and decreased by 30% in subjects consuming less of these foods than normally. The results showed that plasma quercetin is bioavailable from a diet containing berries and indicate that it may be a good biomarker of fruit and vegetable intake in general.

Tangeretin Induces Caspase Dependent Apoptosis and G2/M Arrest in the Erythroleukemia Cell Line K562 In Vitro.

IntroductionTangeretin, a polymethoxyflavon present in citrus peel oil, was found to inhibit Erk-phosphorylation in T47-D breast cancer cells, induce cell death and block invasion in the chick heart invasion assay. Erk-phosphorylation has been implicated in the growth of bcr-abl transformed cell lines as a result of constitutive abl-activation. Here we investigate whether tangeretin can induce apoptosis and growth arrest in the bcr-abl+ erytroleukemia cell line K562, how it affects signal transduction pathways and the balance between pro- and anti-apoptotic proteins.MethodsTangeretin was dissolved in DMSO and used at concentrations up to 100 μM. K562 cells were cultured in RPMI 1640–10% FBS in vitro. Proliferation was followed by MTT test. Apoptosis, cell cycle analysis and bcl-2 expression was assessed by flow cytometry. PARP, Erk1/2, p38, Akt, JNK, p70S6K, and P-p38, P-Akt, P-JNK, and P-p70S6K, bcl-XL and mcl-1 were assessed by Western Blot.ResultsTangeretin shows a time and concentration dependent effect on bcr-abl + K562 cells with a LD50 of 50–70 μM. This effect is accompanied by a G2/M arrest and a significant increase in the percentage of subG0 cells and PARP cleavage at 24 hrs. In short term kinetics (30 minutes) tangeretin inhibits the phosphorylation of Erk. No effect on total Erk1/2, p38, Akt, JNK, p70S6K, and P-p38, P-Akt, P-JNK, and P-p70S6K could be observed. After 24 and 48 hours of treatment, tangeretin is capable of stimulating the phosphorylation of Erk and p70S6K. At the same time activation of procaspase-3 and -9 and downregulation of the anti-apoptotic proteins Mcl-1 and Bcl-xL were seen. Bcl-2 expression was analysed by flow cytometry and was also downregulated.ConclusionThe citrus flavonoid tangeretin is capable of inducing apoptosis and growth arrest in bcr-abl positive K562 cells through activation of caspase-3 and -9 accompanied by a biphasic change in phosphorylation of Erk and p70S6K.

Assessment of lead availability in contaminated soil using isotope dilution techniques

Isotope dilution methods using a stable isotope tracer ( 207Pb) were developed for the determination of Pb availability in contaminated soils. The methods included determination of E values (isotopically exchangeable pool), L values (plant labile pool) and isotopic exchange kinetics (IEK). Isotopically exchangeable Pb was monitored at different exchange times based on measurement of the 207Pb/ 208Pb ratio in soil solution following addition of the tracer. The rate of decrease in the 207Pb/ 208Pb ratio in solution could be described by using the same IEK equation as used previously with radioisotope tracers. The amounts of isotopically exchangeable Pb in Pb-contaminated soils estimated from long-term IEK parameters were in good agreement with directly determined E values up to 15 days. However, values of some of the fitted IEK parameters cast doubts on the validity of using the IEK approach with 207Pb, most probably as a result of irreversible fixation of some of the spike by reactive surfaces in the soils. Estimation of isotopically exchangeable Pb using short-term kinetics data was unsuccessful, substantially underestimating E values. Results for the control (uncontaminated) soil were highly variable, most probably as a result of fixation of tracer by the soil and poor analytical precision due to low solution Pb concentrations. A compartmental analysis of the variation in E values with time indicates a good potential for estimating bioavailable Pb in contaminated soils. The amounts of available Pb obtained from summation of the E 1 min and E 1 min–24 h pools ( E (available)), accounting for an average of 57.62% of total soil Pb, were significantly correlated with both the L values and with Pb extracted from soil with EDTA.

The Effect of Stress on the Temporal and Regional Distribution of Uranium in Rat Brain after Acute Uranyl Acetate Exposure

Long-term exposure to depleted uranium (DU) has been shown to increase brain uranium and alter hippocampal function; however, little is known about the short-term kinetics of DU in the brain. To address this issue, temporal and regional distribution of brain uranium was investigated in male Sprague-Dawley rats treated with a single intraperitoneal injection of 1 mg uranium/kg as uranyl acetate. Due to the inherent stress of combat and the potential for stress to alter blood–brain barrier permeability, the impact of forced swim stress on brain uranium distribution was also examined in this model. Uranium in serum, hippocampus, striatum, cerebellum, and frontal cortex was quantified by inductively coupled plasma–mass spectrometry (ICP-MS) at 8 h, 24 h, 7 d, and 30 d after exposure. Uranium entered the brain rapidly and was initially concentrated in hippocampus and striatum. While multiple phases of uranium clearance were observed, overall clearance was relatively slowand the uranium content of hippocampus, cerebellum, and cortex remained elevated for more than 7 d after a single exposure. Prior exposure to stress significantly reduced hippocampal and cerebellar uranium 24 h postexposure and tended to reduce uranium in all brain regions 7 d after exposure. The application of stress appeared to increase brain uranium clearance, as initial tissue levels were similar in stressed and unstressed rats.The authors thank Mark Morales, Michael Kopplin, and Melinda Pomeroy for their help with this project. This work was supported by U.S. Army Medical Research and Materiel Command DAMD17-01-1-0775. This work does not necessarily reflect the position or policy of the U.S. government.

Elevated extracellular calcium levels induce smooth muscle cell matrix mineralization in vitro

Hyperphosphatemia, elevated calcium x phosphorus product (Ca x P), and calcium burden, major causes of vascular calcification, are correlated with increased cardiovascular morbidity and mortality in dialysis patients. To address the underlying mechanisms responsible for these findings, we have utilized an in vitro human smooth muscle cell (HSMC) model of vascular calcification. Previous studies using this system demonstrated enhanced calcification of HSMC cultures treated with phosphorus levels in the hyperphosphatemic range, and implicated a sodium-dependent phosphate cotransport-dependent mechanism in this effect. In the present study, we examine the effect of increasing calcium concentrations on HSMC calcification in vitro. Increasing calcium to levels observed in hypercalcemic individuals increased mineralization of HSMC cultures under normal phosphorus conditions. Importantly, at these total calcium concentrations, ionized calcium levels increased from 1.2 mmol/L to 1.7 mmol/L, consistent with levels observed physiologically in normocalcemic and hypercalcemic individuals, respectively. Furthermore, increasing both calcium and phosphorus levels led to accelerated and increased mineralization in the cultures. Calcium-induced mineralization was dependent on the function of a sodium-dependent phosphate cotransporter, since it was inhibited by phosphonoformic acid (PFA). While elevated calcium did not affect short-term phosphorus transport kinetics, long-term elevated calcium treatment of HSMCs induced expression of the sodium-dependent phosphate cotransporter, Pit-1. These studies suggest that elevated calcium may stimulate HSMC mineralization by elevating Ca x P product and enhancing the sodium-dependent phosphate cotransporter-dependent mineralization pathway previously observed in HSMCs.

Ischemia-modified albumin during skeletal muscle ischemia.

Ischemia-modified albumin (IMA) has been proposed as a biological marker of myocardial ischemia (1)(2). Exposure to ischemic myocardium modifies circulating albumin at its NH2 terminus by different mechanisms, and this modification is the basis of IMA measurement by the albumin cobalt binding (ACB) test (3). The tissue-specific nature of the mechanism by which ischemia modifies albumin remains undetermined. Together with a nondiagnostic electrocardiogram and negative troponin values, IMA concentrations within the reference interval have high negative predictive value of myocardial ischemia in patients with suspected acute coronary syndromes (1)(2). However, IMA cardiospecificity has not been validated and needs an evidence base before routine clinical use. A recent report showed significant IMA increases 24–48 h after a marathon race, with exercise-promoted gastrointestinal and/or delayed skeletal muscle ischemia being evoked as possible causes of such increases (4). However, because IMA has shown rapid kinetics of increase (in minutes) and return to baseline no longer than 12 h after angioplastic procedures (5), long-duration skeletal muscle ischemia (i.e., occurring during marathons) does not appear to be the most appropriate model to investigate the effect of such ischemia on IMA values or the kinetics of IMA occurring during acute coronary syndromes. The aim of this work was to analyze the possible contribution of skeletal muscle ischemia to IMA by investigating its short-term kinetics in an isolated skeletal-muscle ischemia model. Because lactate and ammonia concentrations increase sharply after a forearm ischemia test, their possible influence in the ACB assay was studied. Ten healthy volunteers (4 men and 6 women) from our laboratory staff (age range, 48–61 years; median, 53 years) with no personal or family history of cardiovascular disease and no known cardiovascular risk factors after a medical examination underwent a forearm ischemia test (6). Briefly, after an overnight fast (10–12 …

Application of a statistical dynamic model investigating the short-term cellular kinetics induced by riddelliine, a hepatic endothelial carcinogen.

In recent studies, riddelliine, a pyrrolizidine alkaloid, was found to increase rates of replication and apoptosis and induce hemangiosarcoma in the liver of rats and mice. To analyze DNA replication and apoptosis data taken from the same animals, we have developed a predictive mathematical model for describing BrdU labeling and apoptotic processes. The model allows the incorporation of simple diurnal patterns in cellular kinetics and is applied to data on hepatocytes and endothelial cells taken from riddelliine exposed rats. Predictions from the model were used with multivariable nonlinear regression techniques to estimate replication and apoptotic rate constants for both cell types and all treatment groups. Hypothesis tests were used with the predicted rates to separate the competing effects of riddelliine on replication and apoptosis of hepatocytes and endothelial cells as well as compare replication rates between cell types. That estimated replication rates were found to be significantly higher for endothelial cells supports the supposition of induction of hemangiosarcoma by riddelliine in the liver.

Single oral doses of 13C forms of pteroylmonoglutamic acid and 5-formyltetrahydrofolic acid elicit differences in short-term kinetics of labelled and unlabelled folates in plasma: potential problems in interpretation of folate bioavailability studies.

Single (13)C6-labelled doses of pteroylmonoglutamic acid (PteGlu; 634 nmol) or 5-formyltetrahydrofolic acid (431-569 nmol) were given to fasted adult volunteers, and the rise in total and (13)C-labelled plasma 5-methyltetrahydrofolic acid metabolite monitored over 8 h by HPLC and liquid chromatography-MS. The dose-adjusted area under the curve (AUC) for total (labelled plus unlabelled) plasma 5-methyltetrahydrofolic acid following a 5-formyltetrahydrofolic acid test dose was 155 % that obtained following a PteGlu test dose. Surprisingly, an average 60 and 40 % of the total plasma 5-methyltetrahydrofolic acid response to [(13)C6]PteGlu and [(13)C6]5-formyltetrahydrofolic acid, respectively, was unlabelled; an observation never before reported. Short-term kinetics of plasma [(13)C6]5-methyltetrahydrofolic acid showed a slower initial rate of increase in plasma concentration and longer time to peak following an oral dose of [(13)C6]PteGlu compared with that for an oral dose of [(13)C6]5-formyltetrahydrofolic acid, while the [(13)C6]5-methyltetrahydrofolic acid AUC for [(13)C6]5-formyltetrahydrofolic acid was 221 % that for [(13)C6]PteGlu. These data indicate that PteGlu and 5-formyltetrahydrofolic acid, which are thought to be well absorbed (about 90 %) at physiological doses, exhibit dramatically different rates and patterns of plasma response. A limitation in the rate of reduction of PteGlu before methylation could result in slower mucosal transfer of [(13)C6]5-methyltetrahydrofolic acid derived from [(13)C6]PteGlu into the plasma. This, when coupled with an observed similar plasma clearance rate for [(13)C6]5-methyltetrahydrofolic acid metabolite derived from either folate test dose, would yield a comparatively smaller AUC. These findings suggest potential problems in interpretation of absorption studies using unlabelled or labelled folates where the rate of increase, the maximum increase, or the AUC, of plasma folate is employed for test foods (mainly reduced folates) v. a 'reference dose' of PteGlu.

"Nonavailable" soil cadmium is bioavailable to snails: evidence from isotopic dilution experiments.

Isotopic dilution techniques were initially used to evaluate the bioavailability of trace metals contained in soils to plants, i.e., the phytoavailability. Here, we use for the first time an isotopic technique to evaluate the zooavailability of cadmium (Cd), i.e., the bioavailability to an animal organism. A terrestrial invertebrate, the snail Helix aspersa, was exposed for 14 days to a polluted soil that was spiked with 109Cd. Isotopic composition of snail tissues was then determined, allowing the computing of the L value, which can be considered as a biological estimate of the bioavailable Cd pool in the soil. It showed that the bioavailable pool of Cd to H. aspersa represented 58% of the total soil Cd. The Evalue, a chemical estimate of the soil Cd labile pool, was calculated with short-term isotopic exchange kinetics experiments and a time-dependent model describing the isotopic exchange over time. The E(14 days) value indicated that the labile soil Cd pool represented 49.6% of the total soil Cd. The L value was significantly higher than the E value, showing that snails accessed the nonlabile soil Cd pool, generally considered as nonbioavailable. The nonlabile pool contributed for 16% to the total Cd accumulated by snails. These results showed that the uptake of Cd in the nonlabile pool by soil organisms could be important and should be considered in risk assessment procedures for metal polluted soils.

Uptake kinetics of arsenic species in rice plants.

Arsenic (As) finds its way into soils used for rice (Oryza sativa) cultivation through polluted irrigation water, and through historic contamination with As-based pesticides. As is known to be present as a number of chemical species in such soils, so we wished to investigate how these species were accumulated by rice. As species found in soil solution from a greenhouse experiment where rice was irrigated with arsenate contaminated water were arsenite, arsenate, dimethylarsinic acid, and monomethylarsonic acid. The short-term uptake kinetics for these four As species were determined in 7-d-old excised rice roots. High-affinity uptake (0-0.0532 mM) for arsenite and arsenate with eight rice varieties, covering two growing seasons, rice var. Boro (dry season) and rice var. Aman (wet season), showed that uptake of both arsenite and arsenate by Boro varieties was less than that of Aman varieties. Arsenite uptake was active, and was taken up at approximately the same rate as arsenate. Greater uptake of arsenite, compared with arsenate, was found at higher substrate concentration (low-affinity uptake system). Competitive inhibition of uptake with phosphate showed that arsenite and arsenate were taken up by different uptake systems because arsenate uptake was strongly suppressed in the presence of phosphate, whereas arsenite transport was not affected by phosphate. At a slow rate, there was a hyperbolic uptake of monomethylarsonic acid, and limited uptake of dimethylarsinic acid.

Short-term kinetics of tumor antigen expression in response to vaccination.

The melanoma patient's immune response to tumor has been extensively studied. Yet, the frequently observed coexistence of tumor-associated Ag (TAA)-specific T cells with their target cells in vivo remains unexplained. Loss of TAA expression might contribute to this paradox. We studied TAA expression in metastases by obtaining fine-needle aspirations from 52 tumor lesions in 30 patients with melanoma before and soon after immunotherapy. Limitations due to low amounts of starting material were overcome with a high fidelity antisense RNA amplification method. TAA expression was measured by quantitative real-time PCR of anti-sense RNA. Decrease in gp100/Pmel-17 TAA preceded tumor disappearance in several instances and could be best explained by immune selection because most patients had received gp100/Pmel-17-specific vaccination. Conversely, immune selection was absent in nonregressing lesions. These observations suggest that vaccination, when successful, triggers a broad inflammatory reaction that can lead to tumor destruction despite immune selection. Additionally, lack of clinical response might be attributed to lack of this initiating event rather than immune escape. This study provides an insight into the natural history of tumors and defines a strategy for the characterization of gene expression in tumors during therapy.

THE USE OF ISOTOPIC EXCHANGE KINETICS TO ASSESS PHOSPHORUS AVAILABILITY IN OVERLAND FLOW AND SUBSURFACE DRAINAGE WATERS

The loss of phosphorus (P) on overland flow and subsurface drainage from soils receiving long-term applications of fertilizer and manure has been linked to the accelerated eutrophication of fresh waters. This loss is initiated by the release of P from soil to solution, which for overland flow can be estimated by water extraction and for subsurface drainage waters by 0.01 M CaCl2 extraction. Although this release is rapid, the information available on the kinetics of P loss is insufficient to support improved soil P management. In this study, an isotopic exchange kinetics (IEK) approach was used to assess the effect of two solutions (water and 0.01 M CaCl2) and different soil-to-solution ratios on soil isotopically exchangeable P (Et). Results are described by a compartmental analysis that quantified the amount of P isotopically exchangeable within 1 min (E1min), 30 min (E30min), 24 hr (E24hr), and between 24 hr and 3 months (E24hr-3mo). The quantity of P in each compartment was then compared with the concentration of P in overland flow and subsurface drainage waters. Isotopically exchangeable soil P within 1 min (1:5 soil to solution ratio) was correlated most closely with the concentration of P in overland flow (r2 = 0.84 with water) and subsurface drainage waters (r2 = 0.93 with 0.01 M CaCl2). For overland flow, a significant correlation was maintained at a soil-to-solution ratio of 1:100 for more exchangeable P pools than at other ratios (1:5 or 1:10). Similarly, the relationship between isotopically exchangeable P in 0.01 M CaCl2 (but not Et in water) and subsurface drainage waters P was maintained for exchange times up to 24 hr, reflecting the greater contact period of subsurface drainage water with soil compared with overland flow. The results suggest that the concentration of P in overland flow and subsurface drainage waters is dependent on the rapid or short-term (1 min and <24 hr) kinetics of soil exchangeable P and that the IEK approach can explain, and with further work may predict, the amount of P that can potentially move from agricultural soils to overland flow and subsurface drainage waters.