MDCK Monolayers on Silicon Chips - The Epithelial Barrier Function on a Cellular Level

The MDCK cell line is a general model system for epithelial cells. Insights about the resistance of the trans- and paracellular pathway on a cellular level come from electrical impedance spectroscopy [1]. We now aimed for a direct measurement of the cellular parameters with a variety of techniques to improve theoretical models of the epithelial cell line.(i) The cell-solid distance was determined by fluorescence interference contrast (FLIC) microscopy. (ii) Multi-Transistor-Arrays were used for measuring the thermal fluctuations of extracellular voltage that provide the electrical properties of the distributed resistor-capacitor system, in particular the sheet resistance of the cell-substrate junction. (iii) An alternating voltage is applied to an electrolyte/oxide/silicon capacitor below the cells and phase maps of the transmembrane voltage were measured in three dimensions with a voltage sensitive dye. These maps give resistances and capacitances of a three-dimensional equivalent circuit. In the case of imperfect confluency in comparison to confluent monolayers a surprising shift in distance to the substrate is found. The specific resistance in the junction beneath confluent layers of cells is enhanced. Time resolved measurements with different Na concentrations show an active regulation of the sheet resistance in the junction which can be blocked by inhibition of Na/K/Cl cotransporter. Trans- and paracellular resistances are accessible via transmembrane voltages. Therefore all important parameters on a cellular level can be determined.[1] C. Lo, C. R. Keese, and I. Giaever, Biophys. J., 69 (1995) 2800