Effect of Ingredient Loading on Water Transport Properties of a Vulcanized Natural Rubber Compound

Water transport properties of a vulcanized natural rubber compound are studied as function of ingredient loading using gravimetric method at 800C. Rubber sheets are compounded according to a fractional factorial design of experiment, where ingredients are treated as factors varied at two levels of loading. Weight change during immersion in water is monitored. The maximum uptakes are determined from the sorption curves which showed two distinct slopes of which two uptake rates are estimated. Analysis of variance shows that high loadings of sulfur, asphalt, and used oil significantly increase the maximum uptake and first uptake rate while only sulfur and asphalt significantly increase the second uptake rate. On the other hand, high loadings of reclaimed rubber, calcium carbonate (CaCO3), mercaptobenzothiazole (MBT) significantly decrease the maximum amount of water uptake. Similarly, high loading of mercaptobenzothiazole disulfide (MBTS) significantly decrease the initial uptake rate while high loadings of reclaimed rubber, CaCO3, kaolin clay, and MBT decrease the final uptake rate of rubber compounds.

Dyeing Properties of Lac Dyes for Wool, Silk and Nylon

The dyeing properties of lac dyes for wool, silk and nylon fibers were investigated, and compared in terms of dependence of dye uptake on pH, dyeing rates, and building-up performance as well as color hue and color fastness of dyed fabrics. For all the three fibers, the uptake of lac dyes was greatly influenced by pH, indicating that the electrostatic interaction between lac dyes and fibers predominantly contributes to lac adsorption. The maximum adsorption wavelength of dyed fabrics shifted to a higher value with increasing application pH, indicating the existence of bathochromic effect. Lac dyes showed the quickest initial uptake rate for silk, the slowest rate for wool. The capacity of lac uptake by three fibers was in the following order: wool > silk > nylon, this being in accord with the quantity of amino groups in these fibers. Dyed wool exhibited the best color fastness.

Characterization of a human plasma membrane heme transporter in intestinal and hepatocyte cell lines

Heme is the most bioavailable form of dietary iron and a component of many cellular proteins. Controversy exists as to whether heme uptake occurs via specific transport mechanisms or passive diffusion. The aims of this study were to quantify cellular heme uptake with a fluorescent heme analog and to determine whether heme uptake is mediated by a heme transporter in intestinal and hepatic cell lines. A zinc-substituted porphyrin, zinc mesoporphyrin (ZnMP), was validated as a heme homolog in uptake studies of intestinal (Caco-2, I-407) and hepatic (HepG2) cell lines. Uptake experiments to determine time dependence, heme inhibition, concentration dependence, temperature dependence, and response to the heme synthesis inhibitor succinylacetone were performed. Fluorescence microscope images were used to quantify uptake and determine the cellular localization of ZnMP; ZnMP uptake was seen in intestinal and hepatic cell lines, with cytoplasmic uptake and nuclear sparing. Uptake was dose- and temperature dependent, inhibited by heme competition, and saturated over time. Preincubation with succinylacetone augmented uptake, with an increased initial uptake rate. These findings establish a new method for quantifying heme uptake in individual cells and provide strong evidence that this uptake is a regulated, carrier-mediated process.

Inhibition of initial transport rate of basolateral organic anion carrier in renal PT by BK and phenylephrine

The effect of ligands for phospholipase C-coupled receptors and of protein kinase C (PKC) stimulation with phorbol ester [phorbol 12-myristate 13-acetate (PMA)] or 1,2-dioctanoyl- sn-glycerol on the activity of the basolateral organic anion transporter (OAT) in S2 segments of single, nonperfused rabbit proximal tubules (PT) was measured with the use of fluorescein and epifluorescence microscopy. The initial uptake rate (25 s, OAT activity) was measured in real time by using conditions similar to those found in vivo. Stimulation of PKC with PMA or 1,2-dioctanoyl- sn-glycerol led to an inhibition of OAT activity, which could be prevented by 10−7 mol/l of the PKC-specific inhibitor bisindolylmaleimide. The α1-receptor agonist phenylephrine as well as the peptide hormone bradykinin induced a reversible decrease of OAT activity, which was prevented by bisindolylmaleimide. The observed effect was not due to a decrease in the concentration of the counterion α-ketoglutarate or to impaired α-ketoglutarate recycling, because it was unchanged in the continuous presence of α-ketoglutarate or methyl succinate. We conclude that physiological stimuli can inhibit the activity of OAT in rabbit PT via PKC. The effect is not mediated by alterations in counterion availability but by a direct action on the OAT.

Dual effect of spermine on mitochondrial Ca2+ transport

1. A dual effect of the polyamine spermine on Ca2+ uptake by isolated rat liver, brain and heart mitochondria could be demonstrated by using a high-resolution system for studying mitochondrial Ca2+ transport. Depending on the experimental situation, spermine had an inhibiting or accelerating effects on mitochondrial Ca(2+)-uptake rate, but invariably increased the mitochondrial Ca2+ accumulation. 2. Both effects were concentration-dependent and clearly discernible on the basis of their different kinetic characteristics. For mitochondria from all three tissues the half-maximally effective concentration for inhibition of the initial rate of Ca2+ uptake was approx. 180 microM, whereas that for the subsequent stimulation of Ca2+ accumulation was approx. 50 microM. 3. Acceleration of the initial uptake rate could be seen when the mitochondria were preloaded with spermine during a 2 min preincubation period and thereafter incubated in a medium without spermine. 4. When such spermine-preloaded mitochondria were incubated in a spermine-containing medium, the increase in Ca(2+)-accumulation capacity was maintained in spite of an unchanged rate of Ca2+ uptake. 5. Mg2+ interacted with the effects of spermine in a differential manner, enhancing the initial inhibition of the rate of mitochondrial Ca2+ uptake and diminishing the subsequent stimulation of mitochondrial Ca2+ accumulation. 6. This dual effect of spermine on mitochondrial Ca2+ transport resolves the apparent paradox that a polycationic compound can act as a stimulator of Ca2+ uptake.

Effect of naphthalene and aqueous crude-oil extracts on the green flagellate Chlamydomonas angulosa. VII. Nitrate and methylamine uptake and retention

Chlamydomonas angulosa grows equally well on nitrate and ammonium as sources of nitrogen. The presence of ammonium decreases nitrate uptake by less than 10% in short-term experiments. The presence of nitrate has no significant effect on short-term uptake of the ammonium analogue methylamine. Cells grown in nitrate media possess considerable methylamine uptake capacity during early exponential growth. This uptake capacity falls rapidly as the cells enter the declining growth phase. When cells are transferred to nitrogen-deficient media, the uptake capacity for methylamine increases threefold to fourfold in 24 h. The half-saturation constants (Km) for nitrate and methylamine uptake of this alga are 0.4 mM and 90 μM, respectively. When C. angulosa cells are transferred from control Bolds basal medium (BBM) to 50% naphthalene saturated or aqueous crude oil saturated media, the initial uptake rate for nitrate increases by a factor of two or decreases by a factor of one-third, respectively, as compared with that of cells transferred to control BBM. However, cells incubated in closed incubation systems with naphthalene or aqueous crude oil saturated media for 3 days lose nitrate when resuspended in control media. Cells transferred to media containing naphthalene up to 20% saturation show no immediate decrease in methylamine transport, while higher naphthalene concentrations cause an immediate decrease in transport activity. However, cells incubated in 50% naphthalene saturated media in a closed system for 2–4 h actually show increased methylamine transport activity when the incubation system is opened to allow escape of the hydrocarbon. Prolonged exposure to 50% naphthalene saturated media, however, causes progressive loss of transport activity.

Kinetics of Lampricide (TFM, 3-trifluoromethyl-4-nitrophenol) Residues in Model Stream Communities

The bioconcentration and elimination rates of lamprey larvicide, 14C-TFM (3-trifluoromethyl-4-nitrophenol), were determined for 20 plant and animal species during experimental lamprey control treatments in six indoor model streams. A two-component curve consisting of a rapid initial uptake rate during the first 2 h followed by a reduced linear rate for the remainder of the 24-h exposure best describes the uptake curve for all species examined. The bioconcentration factors (BCF) ranged from 1.1 to 95.5 for animal components and from 0.7 to 12.2 for the plant species. Macroinvertebrate species with soft, relatively permeable integuments accumulate significantly higher residue concentrations (mean BCF = 45.0) than those species with hard chitinized or calcareous exoskeletons (mean BCF = 11.9). Rates of uptake during the linear phase range from 0.36 μg∙g−1∙h−1 for the crayfish Orconectes propinquus to 17.9 μg∙g−1∙h−1 for the caddisfly larvae Brachycentrus americanus.Rates of loss of TFM accumulations correlate with water current and substrate associations. The mean half-life of TFM is 17.8 h for riffle species and 105.9 h for pool-dwelling species. Half-life figures vary from 7.2 h for the crayfish to 5295 h for annelid worms. The longer half-lives observed for several pool species suggest continued accumulation of 14C-labeled residues from the organic matter of the pool bottoms.

PERIODIC CHANGES IN RATE OF AMINO ACID UPTAKE DURING YEAST CELL CYCLE

Uptake of amino acids is a complex process but in cells growing with ammonia as sole nitrogen source the initial uptake rate of amino acids is a measure of the transport capacity of the uptake system (permease). In synchronous cultures of Saccharomyces cerevisiae amino acids were transported at all stages of the cell cycle. However, for any one amino acid the initial uptake rate was constant for most of the cycle and doubled during a discrete part of the cycle. Thus, for a variety of amino acids the functioning amino acid transport capacity of the membrane doubles once per cycle at a characteristic stage of the cycle. Arginine, valine, and phenylalanine exhibit periodic doubling of uptake rate at different stages of the cell cycle indicating that the transport of these amino acids is mediated by three different systems. Serine, phenylalanine, and leucine exhibit periodic doubling of the uptake rate at the same stage of the cycle. However, it is unlikely that serine and phenylalanine share the same transport system since the uptake of one is not inhibited by the other amino acid. This phenomenon is analogous to the periodic synthesis of soluble enzymes observed in S. cerevisiae.