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[39] Scanning electrode localization of transport pathways in epithelial tissues

1989; Academic Press; Linguagem: Inglês

10.1016/s0076-6879(89)71042-9

1557-7988

J. Kevin Foskett, Carl Scheffey,

Microfluidic and Bio-sensing Technologies

This chapter describes the scanning electrode localization of transport pathways in epithelial tissues. Scanning micropipet methods measure voltage gradients in the medium above the epithelial surface. The voltage gradients are interpreted either implicitly or explicitly as current densities. The conversion factor from voltage gradient to current density is the conductivity of the medium, so that interpretation of the measurement as absolute current density is always subject to an assumption about the local conductivity of the medium. The rationale of the technique is that by measuring a voltage gradient over a short enough distance, close enough and perpendicular to the tissue surface, a good representation of the current density through the epithelial surface is obtained. The physics of electric fields implies that the representation becomes perfect as the distance approaches zero. Unfortunately, the signal-to-noise ratio concomitantly goes to zero. Thus, finite distances must be used, which places a limitation on the spatial resolution—that is, transepithelial current away from the point of recording contributes to the measurements. The extracellular recording approach has been taken using essentially two different methodologies in which either electrolytefilled glass microelectrodes or metal-filled electrodes have been employed.