Genetically encoded voltage indicators

Lipid membranes that form the surface of cells and organelles typically separate fluids of different ion compositions. Differences in ion concentrations and selective ion permeability create a voltage across the membrane. Neurons, muscles, and some secretory cells use fast regenerative changes in this membrane voltage (i.e., action potentials) as signals of inter-and intracellular communication or to trigger muscle contraction or release of biochemical substances. In other, “nonexcitable” cells and organelles, membrane voltage drives important biological processes such as the transport of ions and metabolites across the membrane and the production of ATP in mitochondria.