Membrane intercellular measurement

FIGURE 4.3 High magnification transmission electron micrographs of multilamellar membrane structures in the intercellular space of the cornified part of human epidermis. (A) cryo-electron micrograph of vitreous section. (B, C) conventional electron micrographs of resin embedded sections. The cell plasma membranes appear as 3.8 nm wide bilayers in (A) (open white arrow). A 16 nm broad zone of electron dense material, the cornified cell envelope (white asterix), is directly apposed to the cytoplasmic side of the bilayer plasma membranes in the native sample (A) (open white arrow). Scale bar 50 nm (A). Scale bars 25 nm (B, C) adapted from measures given in Swartzendruber et al. (1989). (A) reprinted from Norlen (2003). With permission from Blackwell Science Publications. (B, C) reprinted from Swartzendruber et al. (1989). With permission from Blackwell Science Publications. 

As previously discussed, electron, light, and confocal microscopy techniques may be used to visualize the position of electron-dense precipitates, radioactive substances, and fluorescent probes, respectively, in the sample tissue. However, none of these techniques possess the capability both to visualize and to selectively measure the flux of a molecule across the skin. SECM, however, permits the measurement and subsequent imaging of the local flux of an electroactive species across biological membranes. Scott et al. [3] used SECM to investigate the effect of pretreatment of the penetration enhancer sodium dodecyl sulfate (SDS), on the ion transport rate and transport pathways of Fe(CN) across hairless mouse skin. Increasing the time of SDS exposure from 10 min to 30 min increased the overall (porous and nonporous) transport of Fe(CN) by 17-fold. More specifically, the SDS-induced increase in Fe(CN)g transport was found to be associated with nonporous (i.e., intercellular) transport routes, while transport via porous routes was significantly reduced. The fraction of Fe(CN)g transport through pores, as measured by... 

Ras trafficking to cellular membranes can be measured by fluorescence recovery after photobleaching (FRAP) and fluorescence loss in photobleaching (FLIP) (54). Both techniques rely on the expression of fluorescent-labeled Ras proteins to monitor different parameters of Ras movement across and between cellular membranes. FRAP involves photobleaching a membrane subdomain and measuring the kinetics of fluorescence recovery—and hence Ras trafflcking—into the bleached area. With FLIP, a cellular membrane is photobleached repeatedly and the subsequent intercellular movement of the photobleached area is monitored. 

Thus, even for the worst case (apical transport), in our numerical example the apical concentration is only 2 mosM greater than at the channel mouth. Nevertheless, solute polarization is still substantial with the measured Lp only 20% of the lateral membrane Lp. This means that the absence of perceptible standing gradients does not guarantee negligible effects of solute-solvent coupling within the lateral intercellular space. 

F. B. LoiseUe and J. R. Casey, Measurement of Intercellular pH , in Methods in Molecular Biology (Totowa, NJ, United States), ed. Q. Yan, Humana Press Inc., 2010, Vol. 637, Membrane Transporters in Drug Discovery and Development, Methods and Protocols, p. 311. 

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