Variation In Uptake Rates Research Articles

Sources and uptake of trace metals in otoliths of juvenile barramundi ( Lates calcarifer)

We conducted an experiment to determine if the concentrations of three trace metals (Cu, Sr, and Pb) in the otoliths of juvenile barramundi ( Lates calcarifer) were related to their concentrations in the water or diet. Fish were kept in freshwater aquaria for 22 days and either fed diet enhanced with 10 μg g −1 Cu, Sr or Pb, or had 10 mg l −1 (Sr and Pb) or 0.5 mg l −1 Cu added to the water. A control group were then transferred to seawater and maintained for a further 83 days. The otoliths were initially ablated for five trace metals (Li, Cu, Sr, Ba and Pb) with LA-ICPMS. Ablation intervals corresponded to between 7 and 11 days of growth. There was no detectable increase in the otolith concentration of any metal for the fish in the enhanced-diet treatments. There was significant uptake of the three metals added to the water (Cu, Sr and Pb). Three (Sr and Pb) or six fish (Cu) were reanalysed with the ICPMS in high-sensitivity mode enabling 5 μm wide ablations to be made at intervals equal to every day or second day during the experiment. These analyses showed that there was considerable variation in uptake rate among individual fish and that the concentration fluctuated widely before an equilibrium concentration was reached after about two weeks exposure. Analysis of the otoliths of the control group of fish that were transferred to seawater showed that the concentration of Li, Sr and Ba in the otoliths varied between the periods of fresh and seawater residency. These variations were related to changes in the concentration of these metals in the water. The fluctuations in Sr concentration were similar to those seen in wild diadromous fish and not as great as those measured in the fish kept in Sr-enhanced water. Sr concentration in the otoliths was strongly negatively correlated with Ba concentration in the experimental fish, but not in wild fish that migrate from the sea into freshwater. Sr/Ca, Ba/Ca and Cu/Ca ratios in the otoliths were positively correlated with water ratios. The partition coefficients of Sr and Ba were similar to published values for marine fish. The concentrations of Li and Pb in the water were below the detection limit in some treatments so no comparisons could be made for these metals. When taken in conjunction with the results of other recent studies of trace metal uptake in otoliths, our data indicate that under experimental conditions, otolith concentrations of several trace metals are related to water concentrations. However, these patterns do not simply extrapolate to the natural environment where the mechanisms involved appear to be more complex.

The uptake of glucose, fructose and sucrose into the lower epidermis of leaf discs of pea (Pisum sativum L. cv. Argenteum)

SUMMARYThe pea mutant, Pisum sativum L. cv. Argenteum, has been used to investigate the sugar uptake characteristics of leaf epidermal tissue. The uptake rates from either 1 mol m−3 glucose, fructose or sucrose into whole leaf discs of cv. Argenteum and of P. sativum cv. Onward were very similar; uptake was linear over a 3 h period, with glucose taken up faster than the other two sugars in both cultivars. A similar pattern for uptake was observed into the lower epidermis of cv. Argenteum. Furthermore, uptake from 1 mol m−3 3‐O‐methylglucose was markedly slower than from 1 mol m−3 glucose. The epidermal tissue showed some day to day variation in uptake rates; however, the basic pattern of uptake was consistent. Kinetic analysis of sugar uptake revealed the presence of two transport components. At concentrations greater than 1 mol m−3 a linear component predominated with fructose entering the epidermis faster than glucose and sucrose. An increase in the pH of the exogenous medium from 5 to 8 caused a slight but steady drop in the rate of uptake of glucose, fructose and sucrose; glucose uptake had a pH optimum of about 5. Glucose and fructose competed with one another and also with sucrose for uptake into the epidermis. Sucrose was not, however, an effective competitor against glucose and fructose. The uptake of glucose, fructose and sucrose was inhibited by about 20–30 % by 0.05 mol m−3 erythrosin B and 1 mol m−3 parachloro‐mercuribenzene sulphonic acid (PCMBS). Carbonyl cyanide m‐chlorophenylhydrazone (CCCP) at 0.05 mol m−3inhibited the uptake of glucose and fructose (60–70%) but did not substantially inhibit sucrose uptake.

Circadian Rhythm in Amino Acid Uptake by Synechococcus RF-1

In the prokaryote Synechococcus RF-1, circadian changes in the uptake of l-leucine and 2-amino isobutyric acid were observed. Uptake rates in the light period were higher than in the dark period for cultures entrained by 12/12 hour light/dark cycles. The periodic changes in l-leucine uptake persisted for at least 72 hours into continuous light (L/L). The rhythm had a free-running period of about 24 hours in L/L at 29 degrees C. A single dark treatment of 12 hours could initiate rhythmic leucine uptake in an L/L culture. The phase of rhythm could be shifted by a pulse of low temperature (0 degrees C). The free-running periodicity was "temperature-compensated" from 21 to 37 degrees C. A 24 hour depletion of extracellular Ca(2+) before the free-running L/L condition reduced the variation in uptake rate but had little effect on the periodicity of the rhythm. The periodicity was also not affected by the introduction of 25 mm NaNO(3). The uptake rates for 20 natural amino acids were studied at 12 hour intervals in cultures exposed to 12/12 hour light/dark cycles. For eight of these amino acids (l-Val, l-Leu, l-Ile, l-Pro, l-Phe, l-Trp, l-Met, and l-Tyr), the light/dark uptake rate ratios had values greater than 3 and the rhythm persisted in L/L.

Uptake of creatine by cultured cells

We have examined the uptake of creatine by cultured monolayers of human IMR-90 flbroblasts, human uterine smooth muscle cells, calf aortic smooth muscle cells, and myoblasts and myotubes of the L 6E 9 rat skeletal muscle cell line. Creatine uptake is dependent on temperature and sensitive to the presence of Na + in the extracellular medium. It is saturable, apparently concentrative, and inhibited by ouabain and structural analogs of creatine. In these respects, it resembles the process of creatine uptake by isolated preparations of skeletal muscle and brain tissues. Lineweaver-Burk plots of the data for variation in rate of uptake with concentration of creatine in the medium are nonlinear, suggesting that the process of uptake may be heterogeneous. Assuming the operation of two saturable processes of uptake, we calculated two values for apparent K m and V for each cell line. Kinetic parameters of creatine uptake by the different cell types are similar. The lower values of K m (0.02–0.04 m m) are in the physiological range of creatine concentration in mammalian plasma.

Variations in the uptake of 3H-norepinephrine during the rat estrous cycle

The rates of 3H-norepinephrine ( 3H-NE) uptake into isolated nuclei-free homogenates from diencephalon were examined in freely cycling female rats of all phases of the estrous cycle. Four time points were investigated in each phase: 12:00, 14:00, 16:00 and 18:00 h. The proestrus and estrus animals displayed no change in uptake rates across the four time points. However, the metestrus and diestrus groups were found to undergo hour to hour variations in uptake rates. In the diestrus group, a significant rise in uptake of 22% was observed from 12:00 to 16:00 h. This increase was followed by a decrease of 21% by 18:00 h as compared to 16:00 h levels. Similarly, a slight increase in uptake was observed in the metustrus animals from 12:00 to 16:00 h. At 18:00 h a 40% decrease from the 16:00 h value was observed. An average of the mean levels of uptake of all phases was calculated for each time point. At 16:00 h an increase in the mean uptake of about 20% was observed when compared to either the 12:00 or the 18:00 h values. Since transmitter reuotake is the major means of terminating receptor activation or inhibition, it is suggested that the above variations in NE uptake may modulate synaptic activity and play a role in the regulation of behavioral and physiological aspects of the estrous cycle.

A method for measuring oxygen uptake rate distributions over the surface zone of excised tissues using a 91-cathode electrode.

Existing methods for measuring the oxygen uptake rates of tissues require amounts of tissue in excess of 20mg or so, and provide no information on spatial variations in uptake rate. The method described here enables estimates of uptake rate to be made at known points on a tissue surface with a spatial resolution of better than 0.5mm.KeywordsUptake RateOxygen Uptake RateMagnetic TapeCathode CurrentTissue SurfaceThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Some observations on the distribution of root activity in apple trees

The distribution of root activity in apple trees was determined by using selective placement of P32 within the rooting volume. In 2-year-old trees of cv Cox/M. 9 absorption of P32 from 30 cm depth was much greater than from 90 cm depth. The rate of absorption over a given period did not seem to be affected by the time of P32 injection. The variation in rate of uptake throughout the season was closely related to the seasonal patterns of white root production measured in a root laboratory. In 25-year-old trees of cv Fortune/M.9 considerable uptake occurred from 90 cm depth both close to the tree trunk and 150 cm away where excavation of a neighbouring tree showed a high root density.