Uptake Of 75Se Research Articles

Transport of Trace Elements through the Hyphae of an Arbuscular Mycorrhizal Fungus into Marigold Determined by the Multitracer Technique

The contribution of the hyphae of an arbuscular mycorrhizal (AM) fungus to the uptake of traceelements by marigold (Tagetes patula L.) was studied using a multitracer consisting of radionuclides of 7Be, 22Na, 46Sc, 51Cr, 54Mn, 59Fe, 56Co, 65Zn, 75Se, 83Rb, 85Sr, 88Y, 88Zr, and 95mTc. Marigold plants colonized and not colonized with Glomus etunicatum were grown for 40 and 60 d in pots with a hyphal compartment separated from the rooting medium by a fine nylon mesh. The multitracer was applied to the hyphal compartment. We found that the uptake of 22Na, 65Zn , 75Se, 83Rb, 85Sr, and 88Y by the mycorrhizal plants was higher than that by the non-mycorrhizal ones. In the case of 95mTc, the uptake by the mycorrhizal plants was similar to that by the control ones. The radioactivity of 7Be, 46Sc, 51Cr, 54Mn, 59Fe, 56Co, and 88Zr could not be detected in any plants. Our results suggest that the AM fungus can absorb Na, Zn, Se, Rh, Sr, and Y from the soil and transport these elements to the plant through its hyphae. The transport ability of the AM fungal hyphae to plant for Be, Sc, Cr, Mn, Fe, Co, Zr, and Tc is likely to be low.

Kinetic analyses of mitochondrial 75selenium uptake in Trigonella foenum-graecum seedlings exposed to selenium and mimosine.

Uptake of (75Se) added in vitro was followed in mitochondria isolated from Trigonella foenum-graecum seedlings grown under different Se status (0.5-1.0 ppm) and with added mimosine (0.1 mM). Uptake of 75Se followed with added Na2 75SeO3 upto 20 microM in the medium was nonlinear in all the groups. Kinetic analyses of the uptake of 75Se for 1 min were carried out for all the groups. The results indicated a cooperative effect during Se transport. Graphical analyses using the Hill plot and Scatchard plot confirmed the existence of negative cooperativity during 75Se uptake. Scatchard plots were biphasic, suggesting the probable presence of two classes of binding sites. The presence of succinate or ATP in the incubation medium inhibited 75Se uptake by 40%. Studies with mitochondrial respiratory inhibitors indicated the uptake to be energy independent. A decrease in the uptake of 75Se by 40% effected by HgCl2, N-ethyl maleimide, and iodoacetate confirmed the interaction of active thiols in the process. The present study confirms the controlled nature of 75Se uptake by plant mitochondria.

Redox modulation of selenium binding proteins by cadmium exposures in mice.

The mechanism of the antagonistic behaviour of selenium (Se) against cadmium (Cd) toxicity is investigated. This study reports the distribution of Cd at the organ and subcellular level after chronic treatments. The possible role of the selenium binding proteins (SBP) during Cd exposure are also evaluated. Kidney concentrates more Cd than liver following 8 weeks of treatment. Simultaneous administration of Se reduced Cd accumulation in Kidney. This affect did not occur in liver. Among the subcellular fractions, the maximum concentrations of both of the elements were found in the cytosol. The overall uptake of 75Se was enhanced in the cytosol of kidney and liver of the Cd treated animals. These observations support a hypothesis that selenium is complexed with cadmium. The increase in the labeling of SBP as a result of Cd exposures may reflect a change in the conformation of the protein molecule. These proteins (SBP) contain a sequence motif, which may be an active redox centre. Also, Cd significantly reduced the glutathione level, thereby disrupting the thiol/disulfide balance. This in turn may affect the redox status of the proteins leading to a 75Se or 75Se-Cd complex with SBP.

Selenium homeostasis in the central nervous system of the rat

These experiments have investigated selenium movement between blood and CNS in anaesthetised rats. Each animal was surgically anaesthetised and the left femoral blood vessels cannulated for blood withdrawal and solute infusion. Each rat received 75-selenium as sodium selenite infused in normal saline and experiments lasted between 5 minutes and 5 hours during which blood samples were periodically taken. At termination, the CNS was removed, regionally dissected and analysed with the plasma samples for 75-Se radioactivity by γ-counting. Data were analysed by graphical analysis. Results showed unidirectional uptake of 75-Se into the CNS and regional differences were not found except for the hypothalamus. On average the CNS influx rate constant (K in) was about 7 ± 1 × 10 −5 ml/min/g. Data suggest that the 75-Se most likely entered the CNS as a free ionic form.

Uptake of 75-Selenium into the central nervous system of the rat.

These experiments have investigated selenium movement between blood and the CNS in anaesthetized rats. Each animal was anaesthetized and the left femoral blood vessels cannulated for blood withdrawal and solute infusion. Each rat received 75-Se as sodium selenite infused in normal saline and experiments lasted between 5 minutes and 5 hours during which blood samples were periodically taken. At termination, the CNS was removed, dissected and analysed with the plasma samples for 75-Se radioactivity by gamma-counting. Data were analyzed by multiple-time uptake analysis. Results showed unidirectional uptake of 75-Se into the CNS and some regional differences were found. On average the CNS influx rate constant (Kin) was about 7 +/- 1 x 10(-5) ml/min/g. This indicates that the 75-Se most likely entered the CNS in a protein-bound form.

Toxicity, metabolism and absorption of selenite by isolated rat hepatocytes

The uptake of various levels of selenite by isolated rat hepatocytes was investigated. The LD 50 value of selenite was about 500 μM. The activity of lactic dehydrogenase in the medium was correlated with cell viability as determined by trypan blue exclusion. After incubation of selenite with hepatocytes, protein-bound Se was the predominant form (80–90% of the cellular Se) present. Subcellular fractionation indicated that most of the radioactivity was present in the cytosol when hepatocytes were incubated with 75Se-selenite. The uptake of 75Se by isolated rat hepatocytes was linear with selenite concentration up to the highest amount tested, 200 μM. Sulfite inhibited the uptake of selenite by hepatocytes.

Subcellular distribution of selenium during uptake and its influence on mitochondrial oxidations in germinatingVigna radiata L

The metabolic significance of Se in plants is not well documented, though the presence of many selenoenzymes in bacteria and the essentiality of Se in higher animals is established. Since germination is an active process in plant growth and metabolism, the effect of Se was investigated in germinating Vigna radiata L, a nonaccumulating Se-deficient legume. Growth and protein were enhanced in seedlings supplemented with selenium (Se) as sodium selenite in the medium up to 1 microgram/mL. The pattern of uptake of 75Se in the differentiating tissues and the subcellular distribution were investigated. The percentage of incorporation of 75Se was greater in the mitochondria at the lowest level (0.5 micrograms/mL) of Se supplementation compared to higher levels of Se exposure. Proteins precipitated from the postmitochondrial supernatant fractions, when separated by means of polyacrylamide gel electrophoresis (PAGE), indicated a major selenoprotein in the seedlings germinated at 2.0 micrograms/mL Se. In seedlings grown with supplemented Se, enhanced respiratory control ratio and succinate dehydrogenase activity were observed in the mitochondria of tissues, indicative of a role for Se in mitochondrial membrane functions.

Kinetic analysis of 75selenium uptake by mitochondria of germinating Vigna radiata of different selenium status.

Earlier studies in our laboratory demonstrated the beneficial role of Se in Vigna radiata, a Se-deficient legume, during germination, as reflected in growth-related parameters and specific uptake of 75Se. Uptake of Na2(75)SeO3, added in vitro by mitochondria isolated from seedlings germinated in control (without Se), and Se-supplemented groups (0.5, 1.0, and 2.0 ppm Se) indicated a proportional increase in the uptake with added Na2(75)SeO3, in concentrations up to 25 microM. The uptake of 75Se, increased linearly with time up to 15 min and a definite efflux followed at 30 min. The results were indicative of cooperative effects during Se transport. Kinetic analyses of the uptake of 75Se during time intervals of 15 and 30 min were carried out both in the whole mitochondria and the mitochondrial protein fractions. Graphical analyses using Lineweaver-Burk plot, Hill plot, log [v] vs log [A] and Scatchard plot confirmed the existence of negative cooperativity during 75Se uptake. Hill coefficient (nH) values were estimated to be around 0.7-0.8. Scatchard plots for 75Se uptake were biphasic, suggesting the probable presence of two classes of binding sites. The number of high and low affinity binding sites were estimated to be around 4-7 and 26-30 nmol/mg protein, respectively. Studies with mitochondrial respiratory inhibitors indicated about 10-20% of the total 75Se uptake to be energy dependent. Inhibition of 75Se uptake by about 60-70% by sulfate and sulfite (5-25 microM) implies the involvement of dicarboxylate port in Se transport. A decrease in the uptake of 75Se by 40-60% effected by CdCl2, HgCl2, mersalyl, and NEM confirmed the interaction of thiols in the process. Evidence for the regulatory nature of 75Se uptake by mitochondria of V. radiata emerges from the present study.

Uptake of selenite, selenomethionine and selenate by brush border membrane vesicles isolated from rat small intestine.

The uptake of selenite, selenate and selenomethionine (SeMet) was performed with brush border membrane vesicles (BBMV) prepared from rats fed selenium-deficient and supplemented diets. At equilibrium (60 min), the uptake of 75Se from [75Se]selenite ranged from 16.5 to 18.9 nmol mg-1 protein. There was a curvilinear relationship in the uptake of selenite over a concentration range of 10-1000 microM. About 2 nmol mg-1 protein was obtained with selenomethionine (SeMet) which occurred between 90 and 180 s. In contrast to selenite, there was a linear relationship in the initial uptake of SeMet over a concentration range of 10-1000 microM. The uptake of selenate was approximately 50-fold lower than selenite, reaching 350 pmol mg-1 protein. Dietary selenium level had no effect on the rate of 75Se accumulation by BBMV. Dramatic differences are found in the uptake and binding of selenium by BBMV incubated with different selenocompounds.

Metabolic relevance of selenium in the insect Corcyra cephalonica. Uptake of 75Se and subcellular distribution.

Requirement, uptake, and subcellular distribution of Na2(75)SeO3 in the larvae of the insect C. cephalonica was investigated. That Se is well tolerated by C. cephalonica upto an added level of 2 ppm in the diet is suggested by the observed increase in body weight, total protein, and succinate dehydrogenase levels. Significant increases in the State 3 respiration ensued with Se supplementation up to 2 ppm in the mitochondrial oxidation of D-glycerol 1-phosphate, succinate and NADH, along with concomitant unaltered State 4 respiration, leading to enhanced RCR values. Maximal uptake of 75Se was registered in the larvae maintained on basal diet when subjected to short-term exposure to 0.5 ppm 75Se level. When exposure level was further increased up to 20 ppm, the observed decrease in the uptake of 75Se suggested that Se status of larvae itself controlled the tissue uptake. Subcellular distribution pattern revealed maximal incorporation of 75Se (cpm/g tissue) in the supernatant fraction, whereas, maximal specific 75Se activity (cpm/mg protein) was associated with the mitochondrial fraction. Autoradiography of the soluble fractions indicated the presence of single selenoprotein in the larval group with short term 2 ppm 75Se exposure. Inherent Se controls both the extent and the nature of distribution of mitochondrial 75Se incorporation. Uptake of 45Ca by the insect mitochondria was enhanced by dietary Se up to 2 ppm but was unaffected by addition of in vitro 75Se in the medium. A more fundamental role for Se in the mitochondrial energy metabolism emerges from these studies.

Stimulation of mucosal uptake of selenium from selenite by some thiols at various sites of rat intestine.

The influence of several thiols (conc. 1 mmol/L) on mucosal uptake of 75Se from 75Se-labeled selenite (conc. 10 mumol/L) across the brush border of rat jejunum and cecum was investigated in vitro using a short-term uptake technique. L-Cysteine (L-Cys) stimulated 75Se uptake in the mid- and distal jejunum and cecum, but not in the proximal jejunum. The effect was maximal in the distal jejunum. D-Cys was less effective in the jejunum and similarly effective in the cecum. L-Leucine (L-Leu) and L-glutamic acid significantly reduced the stimulatory effect of L-Cys on Se uptake in the distal jejunum, whereas the respective effect of D-Cys was not diminished by L-Leu. Cysteamine stimulated mucosal 75Se uptake at all intestinal sites tested, whereas the effect of mercaptopyruvate was restricted to the distal jejunum. Thioglycolate also enhanced 75Se uptake in the distal jejunum. The stimulatory effects of L-Cys, mercaptopyruvate, and thioglycolate were Na(+)-dependent, whereas the effect of cysteamine also occurred in the absence of Na+. Mercaptosuccinate, D-penicillamine, ergothioneine, and thiosulfate did not enhance mucosal 75Se uptake. It is concluded from these findings that the reaction of some thiols with selenite results in Se compounds that are rapidly absorbed by the intestinal epithelium through various Na(+)-dependent and Na(+)-independent mechanisms. The high bioavailability of Se from selenite found by others might thus be the result of the presence of thiols in the gastrointestinal tract.

The uptake and distribution of radioselenium in the larvae of Fasciola hepatica and its snail host Lymnaea columella

Radiolabeled metacercariae of Fasciola hepatica were obtained in vivo by incubating infected Lymnaea columella snails with 20 μCi radioselenomethione ( 75SeM) per snail in 5 ml of water for 5 h, or in vitro by incubating a batch of unlabeled F. hepatica metacercariae with 75SeM for 24 h. Radioassay showed that only 5% of the 75SeM was incorporated into maritas (juvenile flukes) from the in vivo labeled metacercariae. The inner cyst wall of in vivo labeled metacercariae contained 46% of the total activity, of which 21% was dissolved in the excysting medium. The outer, tan-colored cyst wall contained 49% of the radioactivity. Through diffusion/attachment, maritas from in vitro labeled metacercariae could occasionally be labeled with 0.4% of the total radioactivity. However, the activity was lost after inoculation into the body of mice. The outer and inner cyst walls of in vitro labeled metacercariae contained 92% and 7.6%, respectively, of the total activity. Microautoradiography demonstrated that 75SeM was evenly distributed in the body of marita and the cyst wall of inner and outer layers from an in vivo labeled metacercaria. A 9 × 4 μm rectangularly-shaped aggregate of Ag° grains was present on the outer periphery of the inner cyst wall. Microautoradiography of in vitro labeled metacercariae demonstrated a significant concentration of Ag° grains on the cyst walls. The ventral plug contained fewer Ag° grains per unit area compared to the other portion of the inner cyst wall. Uptake and distribution of 75SeM in the snail host were also studied. It appeared that rediae and cercariae tended to concentrate the label in the foot, the mantle and the digestive gland. Little or no radioactivity was present in the areas where F. hepatica larvae were not found.

Uptake of75Se in cataractous rat lens proteins

The purpose of the present study was to measure the pattern of uptake of(75)Se into proteins in normal rat lenses and into the proteins of lenses with selenite-induced cataract. Ten-day-old suckling rats received a single injection of(75)Se with or without a cataractous dose of cold carrier sodium selenite. Four days after injection, the proteins from excised lenses were counted for(75)Se radioactivity and subjected to gel permeation chromatography, amino acid analyses, and mass spectrometry. All three soluble crystallin lens proteins took up(75)Se in both normal and cataractous lenses. However, cataractous lenses did not take up(75)Se into a soluble protein in which major quantities of(75)Se were taken up in normal rats. Futhermore,(75)Se in the gamma-crystallins was associated with an unusual acidic amino acid. It was concluded that selenium metabolism by lens proteins may be unusual compared to other soft tissues.

Selenium metabolism in the dairy cow: the influence of the liver and the effect of the form of Se salt.

1. Six adult Friesian cows were given 75Se as either 75SeO32- or 75SeO42- intravenously. Five of the cows had cannulas in an hepatic vein, the portal vein and one carotid artery to enable the uptake of 75Se by the liver to be measured. Radioactive balance studies were carried out on two of the cows given 75SeO32- and two given 75SeO42-. A seventh cow was given an oral dose of 75Se-labelled barley and the excretion of 75Se in faeces, urine and milk was measured for 14 d. 2. After the injection of 75SeO32- plasma 75Se concentration decreased during the first 30 min with a mean half-life (t 1/2) of 15.6 min. From 30 to 60 min after dosing the concentration of radioactivity increased to reach approximately 50% of the level present 2 min after dosing. Following the injection of 75SeO42- the 75Se was cleared with a mean t 1/2 of 28.5 min during the first 30 min and plasma radioactivity increased only slightly during the next 30 min. 3. during the phase of rapid clearance of 75Se after the injection of 75SeO32- the hepatic venous 75Se concentration was approximately 5% lower than portal venous 75Se concentration. During the period when plasma 75Se activity was increasing the activity in hepatic venous plasma was 3% greater than portal activity. Of the 75Se cleared from plasma after injecting 75SeO32- 40% was calculated to be removed by the liver. 4. After intravenous dosing with 75SeO32- or 75SeO42- approximately 9.5 and 17.0% respectively of the dose injected was excreted in faeces and 10% in urine within 14 d. Almost three times as much 75Se was excreted in urine and 3.5 times as much in faeces during the first 24 h after dosing with 75SeO42- as after 75SeO32-.

The metabolism of [75Se]selenomethionine in four women.

1. The long-term fate of an oral dose [75Se]selenomethionine was studied in four women. 2. Urinary and faecal excretion, respiratory losses and whole-body retention of 75Se were measured, and also 75Se turnover in whole body, plasma and erythrocyte during a period of 33-34 weeks. 3. Intestinal absorption of [75Se]selenomethionine by the four subjects was 95.5-97.3% of the administered dose. 4. Urinary excretion accounted for 6-9% of absorbed 75Se in the first 2 weeks. No radioactivity was detected in expired air.

Developmental and Postdevelopmental Uptake of Dietary Organic and Inorganic Selenium into the Molar Teeth of Rats

The mechanism for the uptake of dietary inorganic and organic selenium by the fully developed, mature molar teeth of mother rats and the developing molar teeth of their pups was studied. Pregnant rats received drinking solutions containing either 0.2 ppm Na2SiO3 plus 0.043 muCi Na2-75SeO3 per ml from day 10 of pregnancy until parturition. Thirteen days postpartum, the uptake of dietary 75Se into developing molar teeth was more extensive than the postdevelopmental uptake onto mature teeth. Developing molar teeth incorporated more 75Se from dietary selenomethionine than from selenite, as did many hard and soft tissues studied. The major portion of 75Se in enamel and dentine was located in the protein fraction of these dental tissues. Dialysis experiments showed that the selenium in enamel and dentine existed in at least three forms: loosely bound selenium, proteinaceous selenotrisulfides, and proteinaceous stable selenium. These data and the results of a previous study (J. Nutr. 103, 553-559) provide evidence that selenium incorporated into developing proteins as selenotrisulfides or selenoamino acids may be responsible for the increases in dental caries reported in man and experimental animals ingesting somewhat increased amounts of dietary selenium.

The value of 75Se-selenomethionine scanning in solitary nodules of the thyroid gland.

This paper describes the use of 75Se-selenomethionine in the study of thyroid nodules. Making use of the different main gamma energies of 75Se and 125I and the short physical half-life of 99Tcm, sequential comparison scanning was carried out in a series of 48 patients with solitary thyroid nodules in which histology was established. Preliminary phantom studies and measurements on a biopsy specimen established that the threshold of detectability of a tumour was 1·5 cm diameter for 75Se and 0·5 cm for 125I. The absorbed dose for the activities used was estimated to be 4·5 rads to the liver and 1·05 rad to the gonads from 150 μCi of 75Se and 30–105 rads to the thyroid gland from 75 μCi of 125I. Eight out of 11 malignant conditions gave positive 75Se-selenomethonine scans. There were only four positive scans in 32 benign conditions and three of these were attributable to physiological or pathological change. The value of the complementary scans was shown in solitary nodules. Diffuse uptake of 75Se-selenomethionine indicated a generalized change in the thyroid. There was no established relationship between the pathology and the intensity of the 75Se uptake. In one case of follicular carcinoma the 45-minute uptake of 75Se was estimated to be 4·8 per cent of the dose above background. The operation specimen contained 18 μCi 125I and 4·6 μCi 75Se per 100 g corrected to scan dates.

In vitro Uptake of Selenium-75 by Red Blood Cells from the Immature Ovine during Varying Selenium Intakes

Six crossbred wether lambs were used for preliminary study of the effect of varying Se intake upon uptake of 75Se in vitro by ovine red blood cells. In a second experiment, 16 crossbred wether lambs were equally allotted among 4 dietary Se levels of 0.014, 0.264, 0.514 and 5.014 ppm. The feeding trial lasted 104 and 107 days for experiments 1 and 2, respectively. Lambs receiving 0.264 and 0.514 ppm Se gained faster, consumed more feed and had a higher feed efficiency than lambs in other dietary groups. Lambs on 0.014 ppm Se performed better than with the 5.014 ppm level. Adequate vitamin E may have prevented deficiency syndromes in lambs fed the low level of Se. Two lambs on the 5.014 ppm level exhibited symptoms of chronic selenosis. The uptake of 75Se was significantly correlated with incubation time in the presence of an O2-CO2 mixture. The initial influx and rate of in vitro uptake of 75Se by ovine blood cells decreased with increasing Se level in the diet. The in vitro uptake of 75Se by red blood cells proved to be a promising technique to assess the nutritional Se status in the immature ovine.

Rate of uptake of 75Se, as selenourea-75Se, in rats in vivo.

Die Geschwindigkeit der Verteilung und Fixierung des Selenharnstoff-75Se wurde in diversen Rattenorganen in vivo und bei Stoffwechselzeiten von 6 h bis zu 14 Tagen untersucht. Die Selenharnstoffmengen varierten zwischen 0,4 und 3,0 mg pro Tier.

Selenium metabolism. II. Effect of injected selenium compounds and of liver injury.

SummaryA 17.5-fold increase of carrier SeO4 did not alter the urinary excretion of 75Se, increased its respiratory excretion and hepatic uptake, but decreased its uptake in other viscera. 75Se accumulation in the liver and pancreas was similar after 75Se-methionine and after 75SeO4 injections. After CCl4 therapy urinary excretion, and renal and pulmonary uptake of 75Se increased. In choline deficient cirrhotic rats urinary excretion of 75Se decreased and visceral, though not the hepatic, uptake of 75Se increased. However, SeO4 supplements reversed these changes in the cirrhotic rats with the exception of the increased renal uptake of 75Se. Over 80% of the non-dialyzable 75Se in the liver accumulated in the mitochondrial and supernatant fractions. The increase of carrier SeO4 was accompanied by an increase of 75Se in the nuclear fraction but did not change the distribution of 75Se in the mitochondrial, microsomal and supernatant fractions. The 75Se uptake increased in the nuclear fraction after CCl4 therap...