Electrical characteristics of mammalian cells on porous supports

The quantification of epithelial barrier functions by measuring the trans-epithelial electrical resistance (TER) and using the Electric Cell-substrate Impedance Sensing (ECIS) has been complicated by the current flowing inside the narrow space underneath cells. This thesis work, by examining the electrical characteristics of epithelial cells on porous supports, is aimed to tackle this problem.; A mathematical model has been constructed to quantify the impedance from the various sources within a cell/electrode system. This model presents three cell-related parameters, α, R_b and C_m: α stands for the impedance contribution from the above-mentioned current underneath cells, R_b is an equivalent representation of epithelial barrier functions and C_m denotes the capacitive impedance of cell membranes. Analysis of the three parameters as well as the electrode impedance (Z _e) has revealed two experimental approaches to reduce or eliminate the complication of α to the deduction of R_b: lowering α down to zero or lowering both Z_e and α.; The experimental realization of the first approach has been studied by examining the electrical characteristics of the African green monkey kidney (BS-C-1) and Madin-Darby canine kidney (MDCK-II) cells on porous filters of mixed esters of cellulose or nitrocellulose. A unique setup featuring a plastic/filter/plastic triple-layer structure was constructed to measure the impedance of cells on filters. With the extremely low α, all the electrical characteristics can be explained by using an equivalent circuit and R_b can be directly obtained from the resistance difference in the low frequency range.; The second approach has been experimentally investigated by examining the electrical characteristics of BS-C-1 cells on porous/rough electrodes, i.e. the gold ECIS electrodes electrochemically coated with conducting polypyrrole/heparin composites or platinum black. Z_e and α, especially the former, were found to be significantly lowered, which greatly reduces the effect of α and yields many new impedance features. R_b can be also directly obtained in a different way from that for the solely lowered α on the non-conducting porous filters.