Cell-affinity test

The long-acting analogue glargine has a somewhat higher affinity to IGF 1 in the cell hue tested... 

C]taurine-labeled MWNTs were administered to mice by three different exposure routes (intravenous injection, gavage, and intratracheal instillation) and their biodistribution was monitored [134], After intravenous injection, [14C]taurine-labeled MWNTs accumulated in the liver, heart, and lung after gavage administration, [14C]taurine-labeled MWNTs was only detectable in the stomach, intestine, and feces. No [14C]taurine-labeled MWNTs were detected in the blood. Finally, [14C] taurine-labeled MWNTs were partly cleared from the lungs after intratracheal instillation. Since various cell and tissue types have demonstrated a high affinity for uptake of taurine, it should be noted that the label used in this investigation may have influenced the biodistribution of the MWNTs tested [101]. 

The Fur protein from E. coli was isolated in one step due to its high affinity for metal-chelate columns loaded with zinc. In DNase footprinting experiments, the Fur protein was shown to bind DNA in the promoter region of several iron-regulated genes. The consensus sequence, called the Fur box, is GATAATGATAATCATT ATC. In vitro binding is dependent on the divalent cations Co2+ Mn2+ /s Cd2+ Cu2+ at 150 iM, while Fe2+ seemed to be less active at this concentration, probably due to oxidation to Fe3+ (De Lorenzo et al., 1987). The unspecificity for divalent metals observed in vitro shows that the cells have to select the ions transported carefully and have to balance their active concentrations. In addition, it is a caveat for the experimenter to test a hypothesis on metal-ion specificity not only in vitro, but also in vivo. 

A very simple technique is to use a radiolabeled ligand (usually a well-known substrate) of the specific transporter of interest. A recent suggestion for functional quantitation of the apparent affinities (fQ values) to P-gp using Caco-2 cells and the substrate taxol has been published [143], The method can be described simply as (1) determination of b —> a transport of3 H -taxol in normal, untreated Caco-2 cells and (2) determination of b —> a transport of 3H-taxol in the presence of verapamil (0.2 mM). The difference between these two components represents the active transport via P-gp. The two concentrations of the test compound are chosen as approximately 0.25 x K, and 4.0 x K, and for the inhibition of taxol transport, and in the study of Gao et al. [143], 16 pM and 250 pM of the test compound were used... 

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