An Electrophysiological Approach to Measure Changes in the Membrane Surface Potential in Real Time

Abstract

Biological membranes carry fixed charges at their surfaces. These arise primarily from phospholipid headgroups. In addition, membrane proteins contribute to the surface potential with their charged residues. Membrane lipids are asymmetrically distributed. Because of this asymmetry, the net-negative charge at the inner leaflet exceeds that at the outer leaflet. Changes in surface potential are predicted to give rise to apparent changes in membrane capacitance. Here, we show that it is possible to detect changes in surface potential by an electrophysiological approach; the analysis of cellular currents relies on assuming that the electrical properties of a cell are faithfully described by a three-element circuit (i.e., the minimal equivalent circuit) comprised of two resistors and one capacitor. However, to account for changes in surface potential, it is necessary to add a battery to this circuit connected in series with the capacitor. This extended circuit model predicts that the current response to a square-wave voltage pulse harbors information, which allows for separating the changes in surface potential from a true capacitance change. We interrogated our model by investigating changes in the capacitance induced by ligand binding to the serotonin transporter and to the glycine transporters (GlyT1 and GlyT2). The experimental observations were consistent with the predictions of the extended circuit. We conclude that ligand-induced changes in surface potential (reflecting the binding event) and in true membrane capacitance (reflecting the concomitant conformational change) can be detected in real time even in instances in which they occur simultaneously.

Temperature dependence of dielectric properties of blood at 10 Hz–100 MHz

“…To further investigate the temperature and frequency dependence of the blood dielectric parameters, we built equivalent circuits with parallel resistors and capacitors based on the multi-order “three-element” equivalent circuit model ( Burtscher et al, 2020 ) or parallel resistors and constant phase angle cells based on the multi-order Cole-Cole equivalent model, as shown in Figure 2 . We estimated the model parameters of the blood complex resistivities using the Zview software ( Zview , 2.70) and assessed the relative error between the absolute values of the complex resistivity calculated by the equivalent circuit model and the measured values using Eq.…”

Development of a Portable Cell-Based Biosensor for the Ultra-Rapid Screening for Boscalid Residues in Lettuce

“…The Bioelectrical Recognition Assay (BERA) employs mammalian cells immobilized in a gel matrix as recognition elements of specific ligands, which either bind to the cells or affect their physiology. The cell–ligand reactions produce measurable electrophysiological responses [ 34 ], since the dynamic changes of the cell membrane potential generate electrical signals [ 35 , 36 ]. The cells’ ability for the specific recognition of the analyte reflects the sensitivity of a BERA biosensing system.…”