Relationships between partition coefficient, uptake rate constant, clearance rate constant and time to equilibrium for bioaccumulation

A simple exponential model is used to interpret the simultaneous uptake and clearance of p,p′-DDT by euphausiids and copepods to and from seawater,[Formula: see text]where [C] and [W] are the concentrations in the organism and seawater, respectively. The clearance rate constant for euphausiids, kj = 0.043/d, is not significantly different from that observed for copepods, 0.048/d. No trend in ki values is detected over the range of p,p′-DDT concentrations in seawater used, 27.8–1388 ng/L. Furthermore, there is a great deal of overlap in the uptake rate constant values between organisms. Uptake rate constants range from 0.76 to 1.21 × 104/d for euphausiids and from 1.04 to 2.51 × 104/d for copepods. There appears to be no need to use a surface-area term if the concentration of p,p′-DDT in the organism is expressed per unit dry weight even though the euphausiids are 2 orders of magnitude larger than copepods. Knowing levels of ΣDDT present in planktonic crustaceans in nature, back calculations suggest that there must be [Formula: see text] ΣDDT/L in seawater. A considerable amount of the ΣDDT reported in seawater must therefore be unavailable to plankters because it is "bound" to particles. Key words: p,p′-DDT, uptake, clearance, surface area, euphausiids, copepods

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Effect of Dopamine Loss and the Metabolite 3-O-Methyl-[18F]Fluoro-dopa on the Relation Between the 18F-Fluorodopa Tissue Input Uptake Rate Constant Kocc and the [18F]Fluorodopa Plasma Input Uptake Rate Constant Ki

Journal of Cerebral Blood Flow & Metabolism ◽

10.1097/00004647-200303000-00005 ◽

2003 ◽

pp. 301-309 ◽

Cited By ~ 4

Author(s):

V. Sossi ◽

J. E. Holden ◽

R. de la Fuente-Fernandez ◽

T. J. Ruth ◽

A. J. Stoessl

Keyword(s):

Rate Constant ◽

Uptake Rate ◽

Uptake Rate Constant

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Effect of Dopamine Loss and the Metabolite 3-O-Methyl-[18F]Fluoro-dopa on the Relation between the 18F-Fluorodopa Tissue Input Uptake Rate Constant Kocc and the [18F]Fluorodopa Plasma Input Uptake Rate Constant Ki

Journal of Cerebral Blood Flow & Metabolism ◽

10.1097/01.wcb.0000050041.22945.3e ◽

2003 ◽

Vol 23 (3) ◽

pp. 301-309 ◽

Cited By ~ 20

Author(s):

V. Sossi ◽

J. E. Holden ◽

R. de la Fuente-Fernandez ◽

T. J. Ruth ◽

A. J. Stoessl

Keyword(s):

Rate Constant ◽

Uptake Rate ◽

Dopaminergic Neurons ◽

Storage Capacity ◽

Synthesis Rate ◽

Positron Emission ◽

Uptake Rate Constant ◽

Downward Bias ◽

Storage Rate ◽

And Storage

Parkinson disease is characterized by the loss of dopaminergic neurons, thus decreasing the system's ability to produce and store dopamine (DA). Such ability is often investigated using 18F-fluorodopa (FD) positron emission tomography. A commonly used model to investigate the DA synthesis and storage rate is the modified Patlak graphical approach. This approach allows for both plasma and tissue input functions, yielding the respective uptake rate constants Ki and Kocc. This method requires the presence of an irreversible compartment and the absence of any nontrapped tracer metabolite. In the case of Kocc, this last assumption is violated by the presence of the FD metabolite 3- O-methyl-[18F]fluoro-dopa (3OMFD), which makes the Kocc evaluation susceptible to a downward bias. It was found that both Ki and Kocc are influenced by DA loss and thus are not pure measures of DA synthesis and storage. In the case of Kocc, the presence of 3OMFD exacerbates the effect of DA egress, thus introducing a disease-dependent bias in the Kocc determination. These findings imply that Ki and Kocc provide different assessments of disease severity and that, as disease progresses, Ki and especially Kocc become more related to DA storage capacity and less to the DA synthesis rate.

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Orthophosphate Uptake Rate Constants are Mediated by the 103–104 Molecular Weight Fraction in Shield Lake Waters

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f84-017 ◽

1984 ◽

Vol 41 (1) ◽

pp. 166-173 ◽

Cited By ~ 13

Author(s):

P. Brassard ◽

J. C. Auclair

Keyword(s):

Molecular Weight ◽

Rate Constant ◽

Uptake Rate ◽

External Solution ◽

Phosphorus Compounds ◽

Phytoplankton Assemblages ◽

Physiological Basis ◽

Colloidal Phosphorus ◽

Uptake Rate Constant ◽

Lake Waters

Although midsummer chlorophyll concentrations can be predicted from total phosphorus, attempts to identify all bioavailable phosphorus compounds has proven difficult. Inconsistencies in determining colloidal phosphorus utilization and the discovery that orthophosphate concentration and flux are poor predictors of lake trophic status has led us to postulate that other forms of phosphorus compounds, which may not be necessarily labeled over the radioisotopic uptake assay (32P) period, are assimilated by natural phytoplankton assemblages. Using ultrafiltration methodology we test the hypothesis that the orthophosphate uptake rate constant can be physiologically varied upon changing the external concentration of selected molecular weight fractions in Shield lake waters. We determined that the fraction between molecular weight 103 and 104 significantly increased the orthophosphate uptake rate constant when exposed to the natural seston. Our discovery suggests that the orthophosphate uptake rate constant is subject to fluctuations depending on the availability of low molecular weight phosphorus metabolites in the external solution. The physiological basis of our observations may be a metabolic coupling between the activity of plasmalemma-bound phosphatases and the transport of PO43− across the cell membrane.

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Uptake of monohydric alcohols by liver: demonstration of a shared enzymic space

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1983.244.2.g198 ◽

1983 ◽

Vol 244 (2) ◽

pp. G198-G214

Author(s):

C. A. Goresky ◽

E. R. Gordon ◽

G. G. Bach

Keyword(s):

Rate Constant ◽

Uptake Rate ◽

Removal Rate ◽

Hepatic Uptake ◽

Multiple Indicator Dilution ◽

Ethanol Infusion ◽

Monohydric Alcohols ◽

Uptake Rate Constant ◽

Anesthetized Dogs ◽

Steady State Levels

Multiple-indicator dilution studies of the hepatic uptake of straight-chain C1-C5 monohydric alcohols were carried out in anesthetized dogs, with either no preceding or saturating infusions of ethanol, and at different steady-state levels for the C2 experiments. Labeled red cells were utilized as a vascular reference, and labeled water was used as a second reference entering liver cells. Kinetic analysis of the data provided estimates of both an uptake rate constant and the space of distribution available to label. From the decrease in the uptake rate constant for labeled ethanol with bulk concentration, we calculated a maximal removal rate of 0.025 mumol X s-1 X (ml liver water)-1 and a Michaelis constant (Km) of 0.32 mM. Especially for the labeled C3-C5 alcohols, a space in excess of that available to water was found, and the bulk of this was dissipated by ethanol infusion. The increment, the "shared enzymic space", which varies with enzymic concentration and inversely with Km, was used to calculate Km values for the other alcohols.

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Chemical and Radiotracer Measurements of Phosphorus Uptake by Lake Plankton

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f83-024 ◽

1983 ◽

Vol 40 (2) ◽

pp. 147-155 ◽

Cited By ~ 65

Author(s):

D. R. S. Lean ◽

E. White

Keyword(s):

Rate Constant ◽

Lake Water ◽

Uptake Rate ◽

Phosphorus Uptake ◽

Small Cells ◽

Phosphate Limitation ◽

Isotope Method ◽

Uptake Rate Constant ◽

Ambient Concentrations ◽

Uptake Velocity

Either chemical or radioisotope methods can be used to measure the maximum uptake velocity for phosphorus in lake water but neither can measure uptake at ambient concentrations. Chemical estimates at ambient concentrations are insensitive and the isotope method provides the uptake rate constant only. By multiplying the uptake rate constant by the ambient phosphate concentration one obtains an estimate for phosphorus influx, but reliable estimates for ambient phosphate concentrations are still unattainable. At added phosphate levels even up to 10 μg P∙L−1, the isotope method overestimates net phosphate uptake because of release of phosphate from the plankton. Influx and efflux are practically equal under steady state conditions, and during periods of phosphate limitation a net uptake of phosphorus occurs only when there is an increase in the phosphorus supply. The uptake of phosphate is predominantly by small cells at low concentrations of added phosphate and by larger cells at the higher enrichments. This makes the use of the radiobioassay for estimating ambient phosphate concentrations difficult to interpret. Furthermore the half-saturation coefficients measured for whole lake water are a mean for the entire population and consist of small values for small algae and bacteria and larger values for larger algae.Key words: phosphorus, kinetics, plankton, algae, bacteria nutrition

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