Permeability tracer

Fluorescein retention measurements are converted to relative amount of fluorescence normalized against protein concentration. Test chemical exposure causing disruption of tight junctions will allow fluorescein molecules to penetrate the comeal tissue and become trapped within its epithelial layer. Thus, fluorescein molecules are used as a permeability tracer and applied in defining comeal epithelial and endothelial permeability (Watsky et al. 1989). FITC-retention provides a quantitative assessment for paracellular leakage... 

The addition of tracer chemicals to an injection fluid provides information on the permeability of a reservoir. Small amounts of a tracer are added to the injected fluid and the distribution of the tracer at the production well is monitored with respect to time. Radioactive tracers and nonradioactive tracers... 

As more sensitive analytical methods for pesticides are developed, greater care must be taken to avoid sample contamination and misidentification of residues. For example, in pesticide leaching or field dissipation studies, small amounts of surface soil coming in contact with soil core or soil pore water samples taken from further below the ground surface can sometimes lead to wildly inaccurate analytical results. This is probably the cause of isolated, high-level detections of pesticides in the lower part of the vadose zone or in groundwater in samples taken soon after application when other data (weather, soil permeability determinations and other pesticide or tracer analytical results) imply that such results are highly improbable. 

A field experiment in a migration study of technetium in the form of TcOj was carried out by Landstrom et al. [64] who injected Tc and radioactive 82Br (non-sorbing tracer) in a highly permeable zone at a borehole. After 10 hours, breakthrough of the tracer was measured, but no retardation, i.e. no reduction of Tc, was observed in comparison with 82Br. 

Capsules were equilibrated with a tracer solution overnight. A capsule pellet (0.2-0.5 ml) was then placed in 5 ml test buffer (PBS or RPMI-1640 medium, Gib-co/BRL, New York, NY) on a shaker and a 0.2-ml aliquot was immediately sampled by a screen-protected pipette with further samples being taken over the next 700 s. The tracer quantity was assayed using the methods described below. A final sample was taken after the capsules has been in contact with the buffer for several hours (equilibrated tracer quantity) and the increment to the tracer concentration at each time was calculated. From the progress of tracer to equilibrium on a semilog plot a slope denoted as the zero -order rate flux constant was obtained and has been used as a measure of capsule permeability. [3H] -Glucose (580 daltons),insulin (6.2 kDa), and ovalbumin (45 kDa) have been used as tracers. Radioactivity was measured by means of a Packard 2000CA Liquid Scintillation Counter (Packard Instruments,... 

Tracer test in KN2RD suggests a permeability barrier rather than limited... 

The detection of a test gas using mass spectrometers is far and away the most sensitive leak detection method and the one most widely used in industry. The MS leak detectors developed for this purpose make possible quantitative measurement of leak rates in a range extending aaoss many powers of ten (see Section 5.2) whereby the lower limit = 10 mbar l/s, thus making it possible to demonstrate the inherent gas permeability of solids where helium is used as the test gas. It is actually possible in principle to detect all gases using mass spectrometry. Of all the available options, the use of helium as a tracer gas has proved to be especially practical. The detection of helium using the mass spectrometer is absolutely ( ) unequivocal. Helium is chemically inert, non-explosive, non-toxic, is present in normal air in a concentration of only 5 ppm and is quite economical. Two types of mass spectrometer are used in commercially available MSLD s ... 

In a discussion of permeability it is important to recognize that we deal with operational definitions, since the act of measurement influences the state of the system. In your case, applying an electrical potential gradient and performing electrodialysis alter the distribution of ionophore within the membrane. I wonder whether you have attempted to measure permeability by isotopic tracer techniques In this method the distribution of ionophore would not be influenced. Furthermore, information can be obtained on the question of carriers versus channels or pores. It should not be difficult to determine the extent of possible isotope interaction between tracer species and abundant species in the membrane as discussed by Kedem and Essig [J. Gen. Physiol., 48, 1047 (1965)]. Positive isotope interaction would tend to suggest the presence of channels or pores, negative isotope interaction the presence of carriers. 

Tracer methods involving chemical markers injected into the contents of the tank may be used. Instrumentation capable of picking up the chemical marker can then determine the presence of a leak caused by seepage of the tracer into the ground. This, like the hydrocarbon sensing method, is genetically referred to as soil vapor monitoring. This method suffers the same weaknesses that have to do with undertank soil permeabilities. 

The Rb-82 generator permits serial studies in the same patient as often as every 10 minutes with 20-60 mCi of Rb-82 for rapid bolus intravenous infusion. Inherent in the administration of high levels of Rb-82 activity is the need for precise flow control from an automated system to deliver the desired amount of radioactivity. The development of the alumina column parameters and the elution protocol as well as the automated microprocessor system controller are presented here. Some of the details of this system have been discussed in earlier publications (15,21). Generator produced Rb-82 is used as a diffusible flow tracer in myocardial perfusion studies and as a nondiffusible tracer in brain studies to assess blood brain barrier permeability changes in patients with brain tumors or Alzheimer s type dementia. 

Defining the movement of water in rocks of low permeability by chemical methods, such as the use of tracers, age dating of water, and isotope ratios, has met with limited success for the same reasons as have the physical methods. That is, they are incapable of describing the permeability distribution in an adequately large area. 

Preston et al. [66] have shown that BBB permeability to the nonmetabolizable, but slowly BBB penetrant, tracer mannitol (182 Da), is between 0.19 and 0.22 pL/g/min in the brain of rats of 1 week of age and this permeability is identical to that of adult rats. The vascular space occupied by the tracer mannitol (the initial volume of distribution Fj) falls from 1.23 mL, at 1 week of age, to 0.75 mL per 100 g brain in the adult rat [66], indicating either a larger vascular volume, resulting from a greater capillary density or capillary diameter in the neonatal rat, or to a significant degree of internalization of the mannitol by the endothelium, possibly by fluid-phase endocytosis into the cerebral capillary endothelial cells in the newborn, compared to the adult. 

More often, carbamates of dextran are prepared by one-step conversion of the polysaccharide with isocyanates or isothiocyanates. This path is especially useful for the conjugation of fluorescent dyes. Fluorescent-marked dextrans are commercial products today. Fluorescent dextran derivatives with different molecular weights and substituents are available as invaluable tracers for studies on microcirculation and vascular permeability in health and disease [8]. Fluorescein isothiocyanate (FITC) dextran (actually the thiocarba-mate) has been well established in this area of research since the 1970s [358]. The isothiocyanate of fluorescein is covalently bound to dextran leading to... 

Figure 5 compares the experimental data with predictions based on the new pore model. The theoretical calculations were done using Equation 6 together with the experimental 3-estradiol solubility data and the experimental ethanol-water concentration gradient data (Figure 4). The partition coefficients in the pores were derived from the solubility data using Equation 4. Henry s law seems to be obeyed, as evidenced by the similar permeability coefficients for 3-estradiol obtained from tracer level as well as saturated solution experiments (Figure 1).

Null Claudin- 5 Claudin- 11 Claudin- 6 Permeability increase of BBB (<800-kDa tracer)... 

For mono-disperse pore size distributions a combination of steady state diffusion and flow permeability measurements can be used to characterize the structural parameters which enable consistent values for tortuosity to be defined. These results can be used to predict the dynamic response of a Wicke-Kallenbach cell to short pulses of a tracer gas having a comparatively high diffusivity and enable a reasonable estimate of the effective diffusion coefficient to be obtained. 

Hore importantly, the response curves are noticeably affected where one or both of the components is adsorbable, even at low tracer concentrations. The interpretation of data is then much more complex and requires analysis using the non-isobaric model. Figs 7 and 8 show how adsorption of influences the fluxes observed for He (the tracer), despite the fact that it is the non-adsorbable component. The role played by the induced pressure gradient, in association with the concentration profiles, can be clearly seen. It is notable that the greatest sensitivity is exhibited for small values of the adsorption coefficient, which is often the case with many common porous solids used as catalyst supports. This suggests that routine determination of effective diffusion coefficients will require considerable checks for consistency and emphasizes the need for using the Wicke-Kallenbach cell in conjunction with permeability measurements. 

D. Brain temperature and blood-brain barrier permeability to hydrophilic tracers. Brain Res. 319,191-212. 

Aside from permeability and absorbency complications, other universal concerns of helium leak detection are factors such as source operating pressure, spraying patterns (for tracer-probe technique), response time, clean-up time, and cold trap usage. Pump use and general helium leak detector maintenance operations are also fairly universal. 

Permeation studies using a number of tracers, including horseradish peroxidase and lanthanum nitrate, have confirmed that the outer third of the epithelium is the rate-limiting barrier for mucosal penetration. When applied to the outer surface of the epithelium, these tracers are seen to penetrate only through the outermost layers of cells. Thus the compacted, flattened cells of the lower superficial layer and intermediate layer present a major physical barrier to transport. The intercellular lipids also play an important role, since extraction of these lipids results in more permeable tissue. Generally, keratinized epithelium appears to be more impermeable than non-keratinized epithelium. 

Another study has classified air between layers of fabrics in clothing assemblies into thin, closed layers and relative thick and extensive layers, and related the thermal resistance of an assembly to the open-air layer, the air permeability, and the air velocity (59). Shivers et al. used a gas tracer technique to demonstrate the importance of microclimate air exchange in thermal comfort of clothing assemblies (60). 

Flux measurements (Schafer et al. 1974). The collection rate (Vc, nl/min) can be measured by the constant bore collection pipette by timed collections. Radioactive tracers can be added to the lumen or bath fluid. For instance, radioactively labelled inulin can be added to the perfusate (Inp) and can be used to measure volume absorption DV = perfusion rate (Vj-Vc). Unidirectional fluxes, bath to lumen and lumen to bath, for any given substance can be quantified, and permeabilities (Px) can be determined ... 

Equilibrium dialysis is used in a number of examples to analyse the ratio of lipid-bound to free analyte. Kramer et al. (1998) described the use of equilibrium dialysis by separating the liposome suspension and the water phase by a semi-permeable membrane. The analyte is dissolved in the water compartment of the system and diffuses into the liposome compartment. If equilibrium is reached, the remaining concentration of the analyte in the water compartment is determined by means of a quantification method (mainly HPLC or LCMS, fluorescence techniques) and the partition coefficient is calculated. Kramer et al. (1997) used a radio tracer substance as analyte to quantify the compound in both compartments using liquid scintillation counting. 

To measure the transport of drugs across the BBB in vitro 2.5 iCi of 3H-labelled drug and 14C-sucrose are applied to each Transwell (in case of 14C-labeled substances, permeability studies are performed with 3H-sucrose). This concentration is high enough to ensure sufficient excess to neglect the decrease of tracer in the donor (apical) compartment during the experiments. Volumes of 1.5 ml in the donor (apical) and 2.5 ml in the acceptor (basolateral) compartment avoid hydrostatic pressure. After addition of the radiolabeled compound, samples of 50 til are taken in duplicate from the basolateral acceptor compartment every 20 min and replaced by 100 xl of fresh assay medium. Cells are kept under culture conditions during the whole transport experiment. Radioactivity is measured after addition of liquid scintillation cocktail in a counter. 

In this table, P represents anions of protein and organic phosphate. The membrane is permeable to the group represented by P. The mean values of the charge on P are -6.7 and -1.08 for the interior and the exterior of the cell, respectively. An electrical potential difference of At// = i/t, t// = 90 mV is measured, i and o denote the intracellular and extracellular, respectively. The activity coefficients of components inside and outside the cell are assumed to be the same, and pressure and temperature are 1 atm and 310 K. Assume that the diffusion flows in from the surroundings are positive and the diffusion flows out are negative. Using tracers, the unidirectional flows are determined as follows ... 

Although it is often assumed that tracer diffusivity can be used as a measure of oxygen permeability, the relationships above show that even for the same tracer diffusivity value at 1 bar, oxygen permeability may be significantly increased if n is less than unity. For example, if n is -1/6 and Pq2 is 10 18 bar, the permeability as given by Eqn. (3) would be increased by a factor of 1000. 

---