Voltage-sensitive fluorescent proteins for monitoring membrane potential

Significant progress in our understanding of neuronal network dynamics underlying brain function requires the ability to monitor the activity of multiple neurons simultaneously. Although optical imaging based on voltage-sensitive dyes offers the spatio-temporal resolution necessary to fulfill this requirement, conventional dyes are not suitable for the labeling of specific cell populations. This fundamental limitation can be overcome by voltage sensors that are genetically encoded and hence targetable to defined cell populations within networks of heterologous cell types.
Even so we began to develop Voltage-Sensitive Fluorescent Proteins (VSFPs) more than a decade ago, a major breakthrough came only with our new series of voltage-sensitive probes based on the voltage sensing domain of the non-ion channel protein Ciona intestinalis voltage sensor-containing phosphatase (Ci-VSP), referred to as VSFP2s, with efficient targeting to the plasma membrane and high responsiveness to membrane potential signaling in excitable cells (He et al, 2007, Dimitrov et al., 2007). Similar to their prototypic precursors (Sakai et al., 2001), VSFP2s are FRET-based. In addition to these second generation voltage sensors, we also developed a third series of voltage-sensitive probes consisting of a single FP reporter (VSFP3s, Lundby et al., 2008) with overall faster response kinetics that are suitable for the optical imaging of fast neuronal signals.
Several color variants of our voltage sensors now exist and allow for the detection of spontaneous subthreshold synaptic potentials as well as single action potentials in both primary cultures of hippocampal neurons and in intact brain tissue.
These newly available genetically-encoded reporters for membrane potential will be instrumental for future experimental approaches directed toward the understanding of neuronal network dynamics and information processing in the brain.