FREQUENCY-DOMAIN IMPEDANCE MEASUREMENTS OF ERYTHROCYTES - CONSTANT PHASE-ANGLE IMPEDANCE CHARACTERISTICS AND A PHASE-TRANSITION

We report measurements of the electrical impedance of human erythrocytes in the frequency range from 1 Hz to 10 MHz, and for temperatures from 4 to 40-degrees-C. In order to achieve high sensitivity in this frequency range, we embedded the cells in the pores of a filter, which constrains the current to pass through the cells in the pores. Based on the geometry of the cells embedded in the filter a circuit model is proposed for the cell-filter saline system. A constant phase angle (CPA) element, i.e., an impedance of the form Z = A/(j-omega)alpha, where A is a constant, j = square-root -1, omega is angular frequency, and 0 < alpha < 1 has been used to describe the ac response of the interface between the cell surface and the electrolyte solution, i.e., the electrical double layer. The CPA and other elements of the circuit model are determined by a complex nonlinear least squares (CNLS) fit, which simultaneously fits the real and imaginary parts of the experimental data to the circuit model. The specific membrane capacitance is determined to be 0.901 +/-0.036-mu-F/CM2, and the specific cytoplasm conductivity to be 0.413 +/- 0,031 S/m at 26-degrees-C. The temperature dependence of the cytoplasm conductivity, membrane capacitance, and CPA element has been obtained. The membrane capacitance increases markedly at approximately 37-degrees-C, which suggests a phase transition in the cell membrane.