DOUBLE-MODE IMPEDANCE ANALYSIS OF EPITHELIAL-CELL MONOLAYERS CULTUREDON SHEAR-WAVE RESONATORS

The viscoelastic behavior of epithelial cells (MDCK-I and MDCK-II) gro wn on AT-cut quartz crystals with a fundamental resonance at 5 MHz was investigated by impedance spectroscopy. Using the electromechanical m odel recently derived by Martin et al. [(1991) Anal Chem 63:2272-2281] for Newtonian liquids in contact with shear wave resonators we quanti fied the viscous damping arising from the adherent cells by fitting th e impedance data with a modified Butterworth-Van Dyke circuit in the r egion of the resonance frequency. Impedance spectroscopy was additiona lly performed in the frequency range from 1 Hz to 1 MHz to scrutinize the passive electrical properties of the epithelial cell layers using an additional platinum electrode. These data allow one to document the cell layers' integrity as well as the electrode coverage. We were abl e to confirm that the presence of a cell-layer mainly increases dampin g of the shear wave and does not exhibit a pure mass-load behavior. Th ese findings were supported by the discovery that the inductance L in the electromechanical model was less influenced by the cell-layer than the resistance R. The apparent cell-viscosities determined by our met hod are 0.097 poise for MDCK-I and 0.142 poise for MDCK-II cell-layers . These low apparent viscosities may be explained in terms of a consid erable spacing between the cells immobilized via their focal contacts and the quartz surface.