The Interactions of P-Glycoprotein with Antimalarial Drugs,Including Substrate Affinity,Inhibition and Regulation

The combination of passive drug permeability, affinity for uptake and efflux transporters as well as gastrointestinal metabolism defines net drug absorption. Efflux mechanisms are often overlooked when examining the absorption phase of drug bioavailability. Knowing the affinity of antimalarials for efflux transporters such as P-glycoprotein (P-gp) may assist in the determination of drug absorption and pharmacokinetic drug interactions during oral absorption in drug combination therapies. Concurrent administration of P-gp inhibitors and P-gp substrate drugs may also result in alterations in the bioavailability of some antimalarials. In-vitro Caco-2 cell monolayers were used here as a model for potential drug absorption related problems and P-gp mediated transport of drugs. Artemisone had the highest permeability at around 50 x 10⁻⁶ cm/sec, followed by amodiaquine around 20 x 10⁻⁶ cm/sec; both mefloquine and artesunate were around 10 x 10⁻⁶ cm/sec. Methylene blue was between 2 and 6 x 10⁻⁶ cm/sec depending on the direction of transport. This 3 fold difference was able to be halved by use of P-gp inhibition. MRP inhibition also assisted the consolidation of the methylene blue transport. Mefloquine was shown to be a P-gp inhibitor affecting our P-gp substrate, Rhodamine 123, although none of the other drugs impacted upon rhodamine123 transport rates. In conclusion, mefloquine is a P-gp inhibitor and methylene blue is a partial substrate; methylene blue may have increased absorption if co-administered with such P-gp inhibitors. An upregulation of P-gp was observed when artemisone and dihydroartemisinin were co-incubated with mefloquine and amodiaquine.     

Methodology for assessing respiration and cellular incorporation of radiolabeled substrates by soil microbial communities

A method is described for determining biodegradation kinetics of both naturally occurring and xenobiotic compounds in surface and sub-surface soil samples. The method measures both respiration and uptake into cellular biomass of¹⁴C-labeled substrates. The estimation of biomass incorporation entailed removal of cells from soil particles by washing the soil with a polyvinyl-pyrrolidone/pyrophosphate solution and H₂O₂. After separation of the cells and the soil particles by centrifugation, the cells were trapped on membrane filters for liquid scintillation counting. Mass balances were easily obtained. The technique was used to measure metabolic activity in soil profiles, including unsaturated and saturated zones. First order rate constants (K₁) were in the range of 10^–3–10^–2 hour^–1 for amino acid metabolism and 10^–5–10^–4 hour^–1 for m-cresol metabolism. Saturation kinetics were observed for amino acids and m-cresol. m-Cresol K₁ values for uptake often exceeded those for respiration by greater than a factor of ten. V_max values were low (amino acids, 10¹–10² ng g^–1 hour^–1; m-cresol, 10^–1 ng g^–1 hour^–1), whereas K_m values were quite high (amino acids, 10³–10⁴ ng g^–1; m-cresol 10³–10⁵ ng g^–1). Saturation was not observed in many horizons even at 10⁵ ng g^–1 dry soil. Frequently, respiration obeyed saturation kinetics whereas uptake was first order. It is concluded that measuring only kinetics of respiration may lead to severe underestimations of biodegradation rates.     

An Abscisic Acid-like Substance in Dry and Soaked Phaseolus vulgaris Seeds Determined by the Lemna Growth Bioassay

An acid inhibitor, probably abscisic acid (ABA) in low concentrations was found to be present in bean seeds. The evidence is based on data from paper electrophoresis, chromatography, UV absorption and growth inhibition in the Lemna bioassay, sensitive down to a concentration of 10^-11M ABA or 0.02–0.03 ng/flask. The inhibitor level as measured by this bioassay decreases considerably with increasing soaking time. Acid ether-soluble inhibitors could even be detected in the soaking water from the soaked seeds.     

Characterization of prostacyclin synthesis in cultured human arterial smooth muscle cells, venous endothelial cells and skin fibroblasts.

The interaction of human platelets with one another and with the blood vessel wall is thought to be regulated in part by a balance between two arachidonic acid metabolites: thromboxane A₂, synthesized by platelets, and prostacyclin (PGI₂), synthesized by the vessel wall. We have studied the ability of cultured human vascular cells to synthesize PGI₂ from arachidonic acid. Four strains of human arterial smooth muscle cells synthesized a mean of 1.36 ng PGI₂ per 10⁵ cells, with a range of 0.2–5.3 ng PGI₂ per 10⁵ cells among the different strains. Human umbilical vein endothelial cells synthesized a mean of 7.16 ng PGI₂ per 10⁵ cells with a range of 2.3–14.0 ng per 10⁵ cells. In contrast, cultured human diploid skin fibroblasts synthesized only 0.27 ng PGI₂ per 10⁵ cells with a range of 0.05–0.6 ng per 10⁵ cells. When cultured cells were mixed with platelets, PGI₂ synthesis from added arachidonate was reduced rather than stimulated. Thus the major precursor cyclic endoperoxides utilized for PGI₂ synthesis are formed within the cells and not from endoperoxides synthesized by platelet cyclooxygenase. Aspirin has been proposed as an anti-thrombotic agent. Aspirin could be ineffective, however, if it inhibited not only platelet cyclooxygenase but that of vessel wall cells as well. Measurement of the rate constant or potency for aspirin inhibition of PGI₂ synthesis in cultured cells indicates that the cyclooxygenase in both cell types of the blood vessel wall is 14–44 fold less sensitive to aspirin inactivation than that in platelets, and appropriate levels of aspirin can selectively block human platelet thromboxane A₂ synthesis without compromising the capacity of the vasculature to produce PGI₂.     

Determination of cobalt in water samples using solidified floating organic drop microextraction coupled with graphite furnace atomic absorption spectrometry

Abstract

A simple, rapid and inexpensive method of the solidified floating organic drop extraction (SFODME) technique coupled with graphite furnace atomic absorption spectrometry (GFAAS) has been developed for the determination of cobalt in water samples. 8-Hydroxyquinoline was used as a complex agent and 1-undecanol was used as the extraction solvent. The factors, including solvent types, solution pH, extractant volume and interfering ions, were investigated and optimised. Under the optimum conditions, the calibration graphs were linear in the range 0.05–10.0 ng mL^-1 cobalt, the limit of detection was 0.02 ng mL^-1, the limit of quantification was 0.05 ng mL^-1 and the relative standard deviation for 10 replicate measurements of 3 ng mL^-1 cobalt was 2.8%. The proposed method was successfully applied for the determination of cobalt in different water samples and the results were satisfactory.     

Cell culture and in vitro studies of fresh and cryopreserved human insulinoma

Summary Dispersed cells from both fresh and cryopreserved human insulinoma have been maintained in cell culture. Initial yield of viable cells was 50% for fresh and 25% for cryopreserved tissue. Viability of cells in culture was documented by increasing numbers of cells (doubling time approximately 5 d initially and 2 d at the sixth subculture for both fresh and cryopreserved tissue) and continued release of insulin over time (approximately 100 ng/ml per 10⁵ cells at 10 d and 175 ng/ml per 10⁵ cells at 30 d of culture for both fresh and cryopreserved tissue). Evidence that cells growing in culture were beta cells was provided by: (a) recovery of intracellular and extracellular immunoreactive insulin (IRI), (b) electron microscopic morphology, and (c) immunohistochemical staining. Cells from fresh insulinoma incubated with increasing concentrations of extracellular glucose released increasing amounts of IRI up to approximately 15 mM glucose, which paralleled changes in plasma insulin obtained during a preoperative glucose tolerance test. Under an Intergovernmental Personnel Act Exchange from the Department of Surgery, University of California, Davis, Sacramento Medical Center.     

High performance liquid chromatography of steroid metabolites in the pregnenolone and progesterone pathways

Rapid separation of gonadal steroids in the progesterone(Δ⁴) and pregnenolone pathway (Δ⁵) has been accomplished by the use of high performance liquid chromatography (HPLC). Two HPLC systems are utilized. The first requires the use of two separate radial compression columns (C-18 and C-8), with steroids being eluted with a methanol-water gradient. The second employs a stainless steel C-18 (reversed phase) column with a 12% octadecylsilane coating. The latter system separates seven of the eight steroids in the Δ⁴ and Δ⁵ pathways in thirty-five minutes. For the quantitation of steroids directly, integration of the peak areas, using 254 nm absorption for the Δ⁴ pathway steroids (5 ng minimum limit), and 210 nm absorption for the Δ ⁵ pathway steroids (25 ng minimum limit) is used. For the quantitation of radiolabeled metabolites resulting from incubation of gonadal tissue with radiolabeled steroid precursors, either one of two methods is used: (1) the eluent can be recovered from the HPLC using a fraction collector, and counted in liquid scintillation counter or (2) the entire eluent (or a portion of it) can be counted immediately by directing the flow through a radioactivity detector.     

A multi-compartment, single and multiple dose pharmacokinetic study of the vaginal candidate microbicide 1% tenofovir gel

Background

Tenofovir (TFV) gel is being evaluated as a microbicide with pericoital and daily regimens. To inhibit viral replication locally, an adequate concentration in the genital tract is critical.

Methods and Findings

Forty-nine participants entered a two-phase study: single-dose (SD) and multi-dose (MD), were randomized to collection of genital tract samples (endocervical cells [ECC], cervicovaginal aspirate and vaginal biopsies) at one of seven time points [0.5, 1, 2, 4, 6, 8, or 24 hr(s)] post-dose following SD exposure of 4 mL 1% TFV gel and received a single dose. Forty-seven were randomized to once (QD) or twice daily (BID) dosing for 2 weeks and to collection of genital tract samples at 4, 8 or 24 hrs after the final dose, but two discontinued prior to gel application. Blood was collected during both phases at the seven times post-dose. TFV exposure was low in blood plasma for SD and MD; median C_max was 4.0 and 3.4 ng/mL, respectively (C≤29 ng/mL). TFV concentrations were high in aspirates and tissue after SD and MD, ranging from 1.2×10⁴ to 9.9×10⁶ ng/mL and 2.1×10² to 1.4×10⁶ ng/mL, respectively, and did not noticeably differ between proximal and distal tissue. TFV diphosphate (TFV-DP), the intracellular active metabolite, was high in ECC, ranging from 7.1×10³ to 8.8×10⁶ ng/mL. TFV-DP was detectable in approximately 40% of the tissue samples, ranging from 1.8×10² to 3.5×10⁴ ng/mL. AUC for tissue TFV-DP was two logs higher after MD compared to SD, with no noticeable differences when comparing QD and BID.

Conclusions

Single-dose and multiple-dose TFV gel exposure resulted in high genital tract concentrations for at least 24 hours post-dose with minimal systemic absorption. These results support further study of TFV gel for HIV prevention.

Trial registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT00561496","term_id":"NCT00561496"}}NCT00561496     

Content of trace elements in the respirable fractions of the air particulate of urban and rural areas monitored by neutron activation analysis

The concentrations (ng/m³) of more than 30 trace elements have been determined in the total air particulate matter and in the sizesegregated fractions collected in urban, industrialized, and rural residential areas in northern Italy by means of a multistage inertial impactor with the PM10 inlet. All measurements have been carried out by instrumental neutron activation analysis, except for Pb and Cd, which have been determined by electrothermal atomic absorption spectroscopy. Analytical quality assurance procedures have been developed with special regard to blanks, reagents, and sampling. Total concentrations and the granulometric distribution found in the different locations are reported and compared.     

The first steps of the light-induced biradical and zwitterion formation from the clusters [Os3(CO)10(α-diimine)] studied with ultrafast time-resolved absorption spectroscopy

The (sub)picosecond time-resolved transient absorption spectra of two triangular [Os₃(CO)₁₀(α-diimine)] clusters have been studied to establish the primary photoprocesses responsible for the formation of biradicals and zwitterions. The TA spectra of [Os₃(CO)₁₀(ⁱPrAcPy)] obtained by excitation into its visible absorption band, show a bleach due to the disappearance of the parent cluster and a new absorption with a maximum at 630 nm. In a non-coordinating solvent the bleach and absorption decay with a lifetime of 25±2 ps but do not disappear completely. The bleach decays to approximately 30% of the initial signal and the transient absorption changes into a much broader absorption without a distinct maximum. The initial transient absorption is assigned to the excited state of the cluster having predominant σ(OsOs)→π*(ⁱPrAcPy) character. From the relaxed excited state the cluster partially decays to the ground state and partially produces biradicals. The lifetime of the excited state does not depend on the solvent as long as it is non-coordinating, but it depends on the energy of this ³σπ* excited state, as observed for [Os₃(CO)₁₀(dmb)]. This effect is attributed to a lowering of the barrier for the reaction from the ³σπ* state. In coordinating acetonitrile (MeCN) the excited state of [Os₃(CO)₁₀(ⁱPrAcPy)] decays double-exponentially. The longer lifetime (τ=21.4 ps) matches that observed in non-coordinating solvents and is assigned to biradical formation. In agreement with previous observations that zwitterion formation in coordinating solvents must occur in the picosecond time domain, the second and faster process (τ=2.9 ps) is assigned for zwitterion formation. These zwitterions are formed by heterolytic splitting of an OsOs bond induced by coordination of MeCN to the Os(CO)₂(ⁱPrAcPy) moiety in the excited state of the cluster. Time-resolved absorption studies in the microsecond time domain showed that the MeCN-coordinated biradicals convert with a lifetime of 13.7 μs into zwitterions. The unique result of this study is that coordinating solvents such as MeCN may induce both homolytic and heterolytic cleavage of a metalmetal bond in such clusters.     

Enkephalin congeners and precursors are synthesized and released by primary cultures of adrenal chromaffin cells

Primary monolayer cultures of bovine adrenal medullary cells contain high levels of enkephalin congeners and their precursors. After six days in culture the levels are (ng/10⁶ cells) 0.82 for sulfoxide Met-enkephalin, 0.12 ng for Met-enkephalin-Lys⁶, 0.18 ng for Met-enkephalin-Arg⁶, 0.88 ng for Met-enkephalin, 0.33 ng for Leu-enkephalin and 1.53 ng for 3et-enkephalin-Arg⁶-Phe⁷. Enkephalin precursors of various M_r ranging from 22,000 to 1,000 were separated by gel filtration. The levels of these precursors remain constant from day 1 to day 6 in culture. Nicotine (5 × 10^?6 M, 5 min.) stimulated the release of these precursors by a Ca⁺⁺-dependent process. A single stimulus released from 3 to 5 % of the total cellular content of the various precursors.     

Characterization,source apportionment,and human health risk assessment of polycyclic aromatic hydrocarbons (PAHs) in road dust of a small island state in the Caribbean

Sixty-four and fifty-six road dust samples were collected over two seasons from various locations throughout the island of Trinidad and analyzed for the 16 priority PAHs. Total PAH concentrations ranged from 21 ng g^?1 to 4723 ng g^?1 (d.w.) for the rainy season and 36 ng g^?1 to 2428 ng g^?1 (d.w.) for the dry season. The Σ4–6 ring PAHs accounted for 88% and 63% of the 16 PAHs in road dust samples for the rainy and dry seasons, respectively. PAH diagnostic ratios, principal component analysis, and cluster analysis revealed both pyrogenic and petrogenic sources in road dust for the two seasons, with major contributions from vehicular emissions. Contributions from incomplete combustion and petroleum sources were also identified. The estimated Incremental Lifetime Cancer Risk (ILCR) associated with exposure to road dust PAHs in Trinidad for the rainy and dry seasons indicated no potential risk for both children and adults, as denoted by ILCR values lower than 10^?6.     

The regulation of liver glycogen synthetase D phosphatase by ATP and glucose

Cortisol at a concentration of 5×10^?6M induces profound changes in U.V. absorption spectra of isolated nuclei from rat liver and thymus. The changes occur within the first 10 min of cortisol action. In both types of nuclei, a blue shift of 5–10 nm from the normal absorption maximum at 260–270 nm is evident. In addition, liver nuclei exhibit an elevation of the spectrum at 230–270 nm (increased U.V. absorption), while the spectrum of thymus nuclei becomes flattened. No such changes occur in nuclei exposed to a physiologically inactive hormone (pregnenolone). The results are interpreted as evidence for cortisol-induced perturbations in deoxyribonucleoprotein structure with consequent changes in the degree of condensation of nuclear chromatin.     

Direct and indirect effects of recombinant human granulocyte-colony stimulating factor on in vitro colony formation of human bladder cancer cells

Although the present experimental use of recombinant human granulocyte-colony-stimulating factor (rG-CSF) has been proven to alleviate the myelosuppression induced by antitumor chemotherapy, it is also believed to stimulate growth of some nonhematopoietic tumor cells. We investigated both the direct and indirect effects of rG-CSF on in vitro colony formation of human bladder cancer cell lines using a modified human tumor clonogenic assay. Peripheral blood mononuclear cells (PBMC) were used as feeder cells (a mixture of 5×10⁴ monocytes/dish and 5×10⁵ lymphocytes/dish obtained from healthy donors). Human bladder cancer cell lines KK-47, TCCSUP and T24, all derived from human transitional-cell carcinomas, were incubated continuously with various concentrations of rG-CSF ranging from 0.01 ng/ml to 10 ng/ml both with and without PBMC for 7–21 days. The concentrations of rG-CSF used were chosen as being in the range of achievable serum concentrations in patients treated with rG-CSF. At the end of incubation, colonies were counted under an inverted phase-contrast microscope, and an increase in the number of colonies in comparison with the control was used to evaluate the effects of rG-CSF. Results were expressed as a percentage of controls. rG-CSF in the upper layer at concentrations ranging from 0.1 ng/ml to 10 ng/ml stimulated the colony formation of all the cancer cell lines tested in the absence of PBMC in the feeder layer, whereas cells with PBMC in the feeder layer were significantly stimulated more than those without PBMC in the feeder layer (P<0.05) up to a certain concentration, which varied from cell line to cell line. At higher concentrations of rG-CSF, no further stimulation but, on the contrary, a decrease in colony formation was observed in cells with PBMC in the feeder layer in all the cell lines tested. Colony formation in KK-47 and T24 cell lines was significantly inhibited at 5 ng/ml and/or 10 ng/ml rG-CSF compared with cells without PBMC in the feeder layer. Our results suggest that rG-CSF may have both direct and indirect stimulatory effects on the growth of human bladder cancer cell lines in vitro. The results obtained also raise the possibility of adverse effects of rG-CSF in bladder cancer patients whose malignant cells may be directly and indirectly stimulated by this factor while it is being used clinically to alleviate the myelosuppression induced by antitumor chemotherapy.     

Application of C stable isotope labeling liquid chromatography–multiple reaction monitoring–tandem mass spectrometry method for determining intact absorption of bioactive dipeptides in rats

The liquid chromatography–multiple reaction monitoring–tandem mass spectrometry (LC–MRM–MS/MS) method using ¹³C stable isotope-labeled dipeptides was newly developed to simultaneously determine the absorption of three antihypertensive peptides (Val-Tyr, Met-Tyr, and Leu-Tyr) into blood of spontaneously hypertensive rats in one run-in assay. After extracting ¹³C-labeled peptides in blood sample with a C₁₈ cartridge, the extract was applied to a ¹³C monoisotopic transition LC–MRM–MS/MS system with d-Val-Tyr included as internal standard. An excellent separation of each dipeptide in LC was achieved at the elution condition of 5–100% methanol in 0.1% formic acid at a flow rate of 0.25 ml/min. The ¹³C-labeled peptides ionized by electron spray were detected in the positive ion mode within 15 min. The established method showed high reproducibility with less than 10% coefficient of variation as well as high accuracy of more than 85%. After the administration of a mixture containing the three ¹³C-labeled dipeptides to rats at each dose of 30 mg/kg, we could successfully determine the intact absorption of each ¹³C-labeled peptide with the maximal absorption amount of 1.1 ng/ml plasma for Val-Tyr by the proposed LC–MRM–MS/MS method.     

Sweroside promotes osteoblastic differentiation and mineralization via interaction of membrane estrogen receptor-α and GPR30 mediated p38 signalling pathway on MC3T3-E1 cells

BackgroundDipsaci Radix has been clinically used for thousands of years in China for strengthening muscles and bones. Sweroside is the major active iridoid glycoside isolated from Dipsaci Radix. It has been reported that sweroside can promote alkaline phosphatase (ALP) activity in both the human osteosarcoma cell line MG-63 and rat osteoblasts. However, the underlying mechanism involved in these osteoblastic processes is poorly understood.PurposeThis study aimed to characterize the bone protective effects of sweroside and to investigate the signaling pathway that is involved in its actions in MC3T3-E1 cells.MethodsCell proliferation, differentiation and mineralization were evaluated by the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay, ALP test and Alizarin Red S staining, respectively. The concentration of sweroside in intracellular and extracellular fluids was determined by ultra-performance liquid chromatography coupled to triple quadrupole xevo-mass spectrometry (UPLC/TQ-XS-MS). Proteins associated with the osteoblastic signaling pathway were analysed by western blot and immunofluorescence methods.ResultsSweroside did not obviously affect the proliferation but significantly promoted the ALP activity and mineralization of MC3T3-E1 cells. The maximal absorption amount 0.465 ng/ml (1.3 × 10⁻⁹ M) of sweroside was extremely lower than the tested concentration of 358.340 ng/ml (10⁻⁶ M), indicating an extremely low absorption rate by MC3T3-E1 cells. Moreover, the ALP activity, the protein expression of ER-α and G protein-coupled receptor 30 (GPR30) induced by sweroside were markedly blocked by both the ER antagonist ICI 182780 and the GPR30 antagonist G15. In addition, sweroside also activated the phosphorylation of p38 kinase (p-p38), while the phosphorylation effects together with ALP and mineralization activities were completely blocked by a p38 antagonist, SB203580. Additionally, the phosphorylation of p38 induced by sweroside were markedly blocked by both the ER antagonist ICI 182780 and the GPR30 antagonist G15.ConclusionsThe present study indicated that sweroside, as a potential agent in treatment of osteoporosis, might exert beneficial effects on MC3T3-E1 cells by interaction with the membrane estrogen receptor-α and GPR30 that then activates the p38 signaling pathway. This is the first study to report the specific mechanism of the effects of sweroside on osteoblastic differentiation and mineralization of MC3T3-E1 cells.     

Development and validation of method for analysis of some ototoxic solvents in saliva matrix by headspace gas chromatography/mass spectrometry

The aim of this study was to develop an analytical method to monitor the saliva matrix for ototoxic solvents absorption: the method is based on headspace gas chromatography/mass spectrometry and represents an alternative biological monitoring for investigating low exposure to hazardous ototoxic solvents. Simultaneous determination of toluene, ethylbenzene, xylenes and styrene has been carried out and the method has been optimized for both instrumental parameters and samples treatment. Chromatographic conditions have been set in order to obtain a good separation of xylene isomers due to the interest in p-xylene as ototoxic one. Method validation has been performed on standards spiked in blank saliva by using two internal standards (2-fluorotoluene and deuterated styrene-d₈). This method showed the possibility to detect the target compounds with a linear dynamic range of at least a 2 orders of magnitude characterized by a linear determination coefficient (r²) greater than 0.999. The limit of detection (LOD) ranged between 0.19 ng/mL (styrene) and 0.54 ng/mL (m-xylene) and the lower limit of quantification (LLOQ) ranged between 0.64 ng/mL (styrene) and 1.8 ng/mL (m-xylene). The method achieved good accuracy (from 99 to 105%) and precision for both intra- and inter-assay (relative standard deviation ranging from 1.7 to 13.8%) for all six compounds concerned. The repeatability was improved by adding sodium sulphate to the matrix. Saliva samples resulted stable for at least 7 days after collection, if stored in headspace vials, at the temperature of 4 °C. An evaluation of the main sources of uncertainty of the method is also included: expanded uncertainties ranges between 10 and 16% for all of the target compounds. In summary, the headspace gas chromatography/mass spectrometry method is a highly sensitive, versatile and flexible technique for the biological monitoring of exposure to ototoxic solvents by saliva analysis.     

Kinetics of iron absorption by excised rice roots

Summary Studies on the rate of iron absorption by excised rice roots from solutions of different concentrations of FeSO₄ showed the presence of two patterns, one in the low (0.005–0.5 mM) and the other in the high (1–30 mM) concentration range. The presence of CaSO₄ or MnSO₄ at 0.5 mM enhanced Fe⁺⁺ absorption in the low concentration range, while CaSO₄ at 10 mM inhibited Fe absorption in the high concentration range in a competitive manner. Fe⁺⁺ absorption at both low and high concentrations was sensitive to metabolic inhibitors. The isotherm for Fe⁺⁺ absorption at O° exhibited an initial absorption shoulder in both low and high concentrations and was suggestive of a latent ion-transport capacity for Fe⁺⁺ in rice roots.     

Evidence that selenium in rat sperm is associated with a cysteine-rich structural protein of the mitochondrial capsules

The keratinous capsules surrounding rat sperm mitochondria were isolated 24 days after intratesticular injections of [⁷⁵Se] selenite or [³⁵S] cysteine. Dodecyl sulfate-polyacrylamide gel electrophoresis of purified, doubly labeled mitochondrial capsules revealed only a single ⁷⁵Se-labeled component, whose molecular weight was 17,000, in agreement with previously reported observations obtained with cruder sperm fractions. Most of the ³⁵S label and the major zone of stained protein on the gels coincided with the position of ⁷⁵Se, suggesting that selenium is associated with a cysteine-rich structural protein. The level of selenium in rat sperm, 195 ± 3.2 ng/10⁸ sperm (approximately 30 ppm), determined by hydride generation and atomic absorption spectrophotometry, is consistent with a structural function for this trace element in the sperm.     

Utility of solid-phase spectrophotometry to determine trace amounts of zinc in environmental and biological samples

A solid-phase spectrophotometric analysis has been proposed for preconcentration and determination of Zn(II) in real samples. The procedure is based on sorption of zinc(II) as 5-(2-benzothiazolylazo)-8-hydroxyquinoline (BTAHQ) complex on dextran-type anion-exchange gel (Sephadex DEAE A-25). The influences of the analytical parameters, including pH of the aqueous solution, amounts of BTAHQ, and sample volume, were investigated. The absorbance of the gel at 675 and 750 nm, packed in a 1.0-mm cell, was measured directly. The molar absorptivities were found to be 2.50 × 10⁷ and 9.55 × 10⁷ L mol⁻¹ cm⁻¹ for 500 and 1000 ml, respectively. Calibration was linear over the range of 0.05–1.10 μg L⁻¹ with a relative standard deviation of less than 1.60% (n = 10). The detection and quantification limits of the 500-ml sample method were 12 and 40 ng L⁻¹ on using 50 mg. For the 1000-ml sample, the detection and quantification limits were 7.5 and 25 ng L⁻¹ using a 50-mg exchanger. Increasing the sample volume can enhance sensitivity. No considerable interferences were observed from other investigated anions and cations on the Zn(II) determination. The proposed method was applied to determine zinc in environmental samples, including natural water, food, certified reference materials, meat, and biological samples, comparing the results simultaneously with those obtained using a flame atomic absorption spectrophotometer, whereby the validity of the method was tested.