Bidirectional experiments

The same quinolone CNV97100 was used to perform bidirectional experiments in Caco-2 cells to obtain the apical to basal Pai, and basal to apical Pya permeabilities at different initial concentrations. The relationship between previously obtained in situ rat permeability values and in vitro Caco-2 of CNV97100 was examined. In each system the in vitro and in situ paracellular permeability of CNV97100 was considered to be negligible. The systems differed in effective surface area (Sj) and in efflux transporter expression level. Although the Caco-2 expression level of P-gp is similar to the expression levels in rat ileum, the model allows for system differences (EJj. 

Bidirectional, experience-depen-dent regulation of N-methyl-D-aspartate receptor subunit composition in the rat visual cortex during postnatal development. Proc. Natl. Acad. Sci. USA 96(22) 12876-80... 

Fig. 4. Time-lapse SFM experiments revealing the growth of single protofibrils and mature fibrils on mica. (A) Fluman amylin protofibrils (adapted from Goldsbury et al., 1999). (B) Bidirectional growth of a single A/ protofibril (adapted from Goldsbury et al., 2005). (C) Unidirectional growth of a mature A/ fibril (adapted from Goldsbury et al., 2005). Scale bar, 200 nm (A, B, and C).

Figure 14. Principle for measuring bidirectional fluxes by 13C metabolic flux analysis. In a carbon labeling experiment, 1 13C glucose is provided in the medium, and the culture is grown until a steady state is reached. Glucose can either go directly via the hexose phosphate pool (Glu 6P and Fru 6P) into starch, resulting in labeling hexose units of starch only at the Cj position, or it can be cleaved to triose phosphates (DHAP and GAP), from which hexose phosphates can be resynthesized, which will result in 50% labeling at both the Ci and the C6 position (assuming equilibration of label by scrambling at the level of triose phosphates). From the label in the hexose units of starch, the steady state fluxes at the hexose phosphate branchpoint can be calculated for example, if we observe 75% label at the Ci and 25% at the C6 position, the ratio of vs to V7 must have been 1 to 1. All other fluxes can be derived if two of the fluxes of Vi, V6, and V7 are known (e.g., V2 vi V3 V5 + v6).

W. Wiechert and A. A. de Graaf, Bidirectional reaction steps in metabolic networks. Part I Modeling and simulation of carbon isotope labelling experiments. Biotechnol. Bioeng. 55,101 117 (1997). 

In a potentiostatic experiment, E is held constant so that, according to eqn. (170), the rate of the electrode reaction depends only on the surface concentrations of the species O and R. One of the simplest circumstances that can be imagined would have the reaction occurring bidirectionally with the forward rate proportional to the concentration of O and the backward rate proportional to the concentration of R, so that... 

Evidence for bidirectional replication is supported by additional experiments. Growing bacteria were briefly ex-... 

Fig. 2 shows some experimental data points of pressure and strain along with the fitted theoretical curve, calculated according to equ. (4). For the figure, the point where the direction of pressure steps was reversed was chosen in order to demonstrate bidirectional response of the sample. The fit represents the measured strains in an excellent way. Note that the pressure steps are relatively large up to 0.3 MPa or 10% of the bulk modulus of the gel. This was probably the cause of a crack appearing in the sample, as was noticed after completion of the experiment. 

Philpot BD, Sekhar AK, Shouval HZ, Bear MF. 2001. Visual experience and deprivation bidirectionally modify the composition and function of NMDA receptors in visual cortex. Neuron 29(1) 157-69... 

This buffer is used in both the unidirectional (permeability) and the bidirectional (Efflux, Section 4.3.2). In the permeability assay, NCEs are placed into the apical compartment of the Transwell. Duplicate samples are taken immediately after compound addition from the apical compartment (zero time) and then after 2h from both the apical and basolateral compartments for LC-MS/MS analysis. The integrity of the monolayer is confirmed by the measurement of the transepithelial electrical resistance (TEER), which must be above a certain limit to be used for transport experiments. In addition, with each experiment a transcellular and a paracellular marker are included for quality control. 

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