Dextran tracer diffusion

The rate of diffusion of molecules through intact tissues in an animal is difficult to measure, so the amount of information currently available is limited. Diffusion coefficients for size-fractionated dextrans, albumin, and antibodies have been measured in granulation tissue and tumor tissue [20, 21] similar measurements have been made in slices of brain tissue [87]. In both cases, the diffusion coefficient was estimated by fitting solutions to the diffusion equation, similar to Equation 3-36, to data obtained by direct visualization of fluorescent tracers in the interstitial space. These measurements, as well as others made by a variety of techniques, are compiled in... 

As part of a study of probe diffusion and tracer chain diffusion in dextran solutions, Furukawa, et al. report the viscosity of 40 and 150 kDa dextrans in aqueous solution(20). Viscosities measured with Ubbelohde viscometers reached 100 cP concentrations extended up to 400 g/1. Their measurements and functional fits appear as Figure 12.4. While t (c) is described reasonably weU by stretched exponentials in c, for solutions of the 150 kDa dextran at small concentrations the measured viscosities clearly lie below the stretched-exponeniial fit. 

To characterize the transport properties of in vitro BBB models, Malina et al. [75] and others [76-84] measured the diffusive permeability of endothehal cell monolayer and coculture of endothelial cells with astrocytes to fluorescence or isotope-labeled tracers, for example, sucrose, inulin, and mannitol. Sahagun et al. [85] reported the ratio between abluminal concentration and luminal concentration of different-sized dextrans (4k, 10k, 20k, 40k, 70k, and 150k) across mouse brain endothelial cells. Gaillard and de Boer [66] measured the permeabihty of sodium fluorescein and fluorescein isothiocyanate (FlTC)-labeled dextran 4k across a cocultirre of calf BCEC with rat astrocytes. Many investigators have measured the TEER of brain endothelial monolayers and cocultures as an indicator of ion permeability [86-89],... 

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