V m -related extracellular potentials observed in red blood cells

Even in nonexcitable cells, the membrane potential V is fundamental to cell function, with roles from ion channel regulation, development, to cancer metastasis. V arises from transmembrane ion concentration gradients; standard models assume homogeneous extracellular and intracellular ion concentrations, and that V only exists across the cell membrane and has no significance beyond it. Using red blood cells, we show that this is incorrect, or at least incomplete; V is detectable beyond the cell surface, and modulating V produces quantifiable and consistent changes in extracellular potential. Evidence strongly suggests this is due to capacitive coupling between V and the electrical double layer, rather than molecular transporters. We show that modulating V changes the extracellular ion composition, mimicking the behaviour if voltage-gated ion channels in non-excitable channels. We also observed V -synchronised circadian rhythms in extracellular potential, with significant implications for cell-cell interactions and cardiovascular disease.