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 rho(J) = r(J)d(J) by combining measurements of the sheet resistance r(J) and of the distance d(J) 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 Omega cm to 750 Omega cm and find that the sheet resistance r(J) is proportionally enhanced, but that the distance is invariant around d(J) = 75 nm. In all cases, the resulting resistivity rho(J) 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.