Uptake kinetics

Fatty Acid Transporters. Figure 2 Quencher-based real-time fatty acid uptake assay with a fluorescently labeled FFA analogue (C1-Bodipy-C12). Predominantly protein-mediated fatty acid uptake by 3T3-L1 adipocytes (diamonds) was compared with diffusion-driven uptake by fibroblasts (squares) using the QBT Fatty Acid Uptake reagent (Molecular Devices Corp., CA, USA), which contains C1-Bodipy-C12 as substrate in conjunction with a cell impermeable quencher. Uptake kinetics was recorded using a Gemini fluorescence plate reader. Error bars indicate the standard deviations from 12 independent wells. RFU relative fluorescence units. 

In vitro and ex vivo studies have shown that FATPs transport LCFAs and very long-chain fatty acids (VLCFAs) but no medium-chain fatty acids, fatty acid esters, or lipid-soluble vitamins [4]. LCFA transport is inhibited by prior protease treatment. Synthetic substrates for FATPs include 14C-labeled fatty acids and the fluorescently labeled fatty acid analogue C1 -BODEP Y-Cl 2. Using the latter substrate, differences in fatty acid uptake kinetics between FATP expressing 3T3 LI adipocytes and 3T3 LI fibroblasts, which are devoid of FATPs, can be readily appreciated (Fig. 2). 

In Figure 33, both the first-order uptake kinetics and the equilibrium plateau levels decrease with increased BSA concentration, indicating that protein binding plays an influential role in the mass transfer process. To put biophysical meaning and quantitation into these observations, the following model is presented. 

Figure 33 Uptake kinetics of PNU-78,517 by MDCK cell monolayers grown on a solid plastic surface as a function of bovine serum concentration in the bathing solution. [Redrawn from Raub et al. (1993) with permission from the publisher.]...

The initial conditions are CD = CD(0) at t = 0 and CR = 0 at t = 0. Efforts to obtain analytical solutions are tedious and unnecessary. By applying the change in concentrations (or mass) in the donor and receiver solutions with time to the Laplace transforms of Eqs. (140) and (141), the inverse of the simultaneous transformed equations can be numerically calculated with appropriate software for best estimates of a, (3, and y. It is implicit here that P Pap, Pbh and Ke are functions of protein binding. Upon application of the transmonolayer flux model to the PNU-78,517 data in Figure 32, the effective permeability coefficients from the disappearance and appearance kinetics points of view are in good quantitative agreement with the permeability coefficients determined from independent studies involving uptake kinetics by MDCK cell monolayers cultured on a flat dish... 

Cellular Uptake Kinetics of LDH-FITC Into Cells... 

Fig. 13.4 Cellular uptake kinetics of LDH-FITC as a function of concentration (A) and incubation time (B) in HOS cells. Cells were incubated with LDH-FITC for2h (A), concentration of LDH-FITC was 200pg/ml (B). The cellular uptake was quantified by flow cytometry.

This model was shown to be applicable for describing moisture uptake kinetics (in vacuum) above RH0 for single-component systems of alkali halides, sugars, and choline salts [31]. The model later was extended to consider the moisture uptake kinetics above RH0 for multicomponent systems of these substances [33]. 

Larsson, O. M., Johnston, G. A. R., and Schousboe, A. (1983) Differences in uptake kinetics of cis-3-aminocyclohexane carboxylic acid into neurons and astrocytes in primary cultures. 

Santana-Casiano, J. M., Gonzalez-Davila, M., Laglera, L. M., Perez-Pena, J., Brand, L. and Millero, F. J. (1997). The influence of zinc, aluminum and cadmium on the uptake kinetics of iron by algae, Mar. Chem., 59, 95-111. 

To describe the dynamics of metals at biological interphases in the presence of various ligands, the kinetics of dissociation of the complexes have to be taken into account in relation to the diffusion and to the uptake kinetics ([14] and Chapters 3 and 10 in this volume). Based on kinetic criteria, labile and inert complexes can be distinguished as limiting cases with regard to biological uptake ([14] and Chapter 3, this volume). 

Button, D. K. (1991). Biochemical basis for whole-cell uptake kinetics specific affinity, oligotrophic capacity, and the meaning of the Michaelis constant, Appl. 

Points of Caution When Interpreting Uptake Kinetics. 491... 

Many experimental variations are possible when performing uptake studies [246]. In a simple experiment for which the cells are initially free of internalised compound, the initial rates of transmembrane transport may be determined as a function of the bulk solution concentrations. In such an experiment, hydrophilic compounds, such as sugars, amino acids, nucleotides, organic bases and trace metals including Cd, Cu, Fe, Mn, and Zn [260-262] have been observed to follow a saturable uptake kinetics that is consistent with a transport process mediated by the formation and translocation of a membrane imbedded complex (cf. Pb uptake, Figure 6 Mn uptake, Figure 7a). Saturable kinetics is in contrast to what would be expected for a simple diffusion-mediated process (Section 6.1.1). Note, however, that although such observations are consistent... 

As discussed in Section 5.1, for saturable uptake of a trace metal, the steady-state process is most commonly described by Michaelis-Menten uptake kinetics [265] ... 

POINTS OF CAUTION WHEN INTERPRETING UPTAKE KINETICS... 

Wheeler, P. A., Gilbert, P. M. and McCarthy. J. J. (1982). Ammonium uptake and incorporation by Chesapeake Bay phytoplankton short term uptake kinetics, Limnol. Oceanogr., 27, 1113-1128. 

Fig. 7.2.1. LAS uptake kinetic curve for different organisms (a) Cn homologue by the marine clam It. semidecussatus (taken from Ref. [21]) (b) C12 LAS by the freshwater fish P. promelas (taken from Ref. [57]).

Szeimies RM, Karrer S, Abels C, Steinbach P, Fickweiler S, Messmann H, Baumler W, Landthaler M (1996) 9-Acetoxy-2,7,12,17-tetrakis-(beta-methoxyethyl)-porphycene (ATMPn), a novel photosensitizer for photodynamic therapy uptake kinetics and intracellular localization. J Photochem Photobiol B 34 67-72. 

PESs by the end of the exposure. Differences in exposure concentrations did not affect the sampling rates of PESs, which indicate that these devices obey first-order uptake kinetics. The sampling rate of " C-2,2 ,5,5 -TCB by PESs (4.8 L d ) was similar to that observed for 1 mL triolein SPMDs, with the same surface area. 

Bartkow, M.E. Hawker, D.W. Kennedy, K.E. Muller, J.K. 2004, Characterizing uptake kinetics of PAHs form the air using polyethylene-based passive air samplers of multiple surface area-to-volume ratios. Environ. Sci. Technol. 38 2701-2706. 

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