The Extracellular Electrical Resistivity in Cell Adhesion

The interaction of cells in a tissue depends on the nature of the extracellular matrix. The electrical properties of the narrow extracellular space are unknown. Here we consider cell adhesion mediated by extracellular matrix protein on a solid substrate as a model system. We culture human embryonic kidney (HEK293) cells on silica coated with fibronectin and determine the electrical resistivity in the cell-solid junction ρJ=rJdJρJ=rJdJ by combining measurements of the sheet resistance rJrJ and of the distance dJdJ between membrane and substrate. The sheet resistance is obtained from phase fluorometry of the voltage-sensitive dye ANNINE-5 by alternating-current stimulation from the substrate. The distance is measured by fluorescence interference contrast microscopy. We change the resistivity of the bath in a range from 66⁡Ω⁡cm to 750⁡Ω⁡cm and find that the sheet resistance rJrJ is proportionally enhanced, but that the distance is invariant around dJ=75⁡nmdJ=75⁡nm. In all cases, the resulting resistivity ρJρJ is indistinguishable from the resistivity of the bath. A similar result is obtained for rat neurons cultured on polylysine. On that basis, we propose a “bulk resistivity in cell adhesion” model for cell-solid junctions. The observations suggest that the electrical interaction between cells in a tissue is determined by an extracellular space with the electrical properties of bulk electrolyte.