See Your Cells in Action: Voltage Imaging Unveiled
"Discover how genetically encoded voltage indicators (GEVIs) light up cellular communication, offering new insights into brain activity and beyond."
Imagine being able to watch the electrical conversations happening inside your cells. That's the promise of voltage imaging, a revolutionary technique that allows scientists to visualize changes in membrane potential—the driving force behind cellular communication. This article explores how genetically encoded voltage indicators (GEVIs) are making this possible, opening new doors in neuroscience and beyond.
Traditional methods for studying electrical activity in cells have limitations. Organic voltage-sensitive dyes, used for decades, lack specificity and can be difficult to apply to certain cell types. GEVIs offer a more targeted approach. By genetically engineering cells to express fluorescent proteins that respond to voltage changes, researchers can observe activity in specific cell populations with unprecedented precision.
This article will guide you through the principles of voltage imaging using GEVIs, highlighting the different types of sensors available and the experimental setup required. Whether you're a seasoned researcher or just curious about the inner workings of cells, this overview will provide a solid foundation for understanding this exciting field.
Broadening Voltage Imaging
Recent advances in genetically encoded voltage indicators (GEVIs), optical instrumentation, and analysis software have brought voltage imaging within reach of most neuroscience labs. The method can resolve subthreshold dynamics and action potentials across scales, from the flickering of single ion channels to large-scale neural population dynamics in behaving animals. However, Bando et al.'s comparative evaluation found that each recently developed GEVI has advantages and disadvantages, with no single indicator ideal for every experiment. A 2017 review likewise reported that current-generation GEVIs remained far from optimal.
GEVIs and Their Limits
Optical voltage imaging commonly uses genetically encoded voltage indicators (GEVIs), supported by optical instrumentation and analysis software. Compared with calcium imaging, extracellular recording, and related approaches, GEVI imaging can address low temporal resolution, lack of cell-type information, and insensitivity to subthreshold membrane-voltage signals. The practical guide describes voltage imaging as capable of resolving both subthreshold dynamics and action potentials across scales. These methods therefore expand access to membrane-voltage measurements, while the cited sources frame their limitations in comparison with established techniques.
What are Genetically Encoded Voltage Indicators (GEVIs)?
GEVIs are essentially fluorescent reporters that change their brightness or color in response to changes in the electrical potential across a cell's membrane. They consist of a voltage-sensing domain linked to one or more fluorescent proteins. When the membrane potential changes, the voltage-sensing domain shifts, altering the fluorescent protein's properties. This allows researchers to 'see' the electrical activity of the cell.
- Single Fluorescent Protein (FP) GEVIs: These use a single fluorescent protein that changes its fluorescence intensity in response to voltage changes.
- Förster Resonance Energy Transfer (FRET)-based GEVIs: These use two fluorescent proteins, a donor and an acceptor. Voltage changes alter the distance or orientation between the proteins, affecting the efficiency of energy transfer (FRET) and changing the relative fluorescence of the donor and acceptor.
- Hybrid GEVIs: These combine a membrane-anchored fluorescent protein with a separate quenching molecule that responds to voltage.
Targeting Indicators to Membranes
Recent work focuses on directing GEVIs to cell membranes so they can measure membrane potential. The review reports that Golgi-to-plasma membrane trafficking signals (Golgi TS) and endoplasmic reticulum export signals (ER ES) can be added to transgenes to enhance transport from the endoplasmic reticulum to the Golgi and ultimately to the cell membrane. Lee et al. (2016) described imaging membrane potential with two types of genetically encoded fluorescent voltage sensors. Together, these sources highlight membrane targeting and sensor implementation as active areas of GEVI research.
The Scaling Challenge
A central difficulty appears when voltage probes move from optically reporting membrane potential in single cultured cells to imaging populations of cells in slices or living animals. The cited study identifies a new challenge at that transition: optically resolving different types of neuronal activity. Population-scale experiments therefore introduce an activity-discrimination problem that is not captured by single-cell demonstrations. This limitation complicates interpretation as the scope of voltage imaging expands.
The Future of Seeing Electricity
Voltage imaging with GEVIs is a rapidly evolving field with immense potential. As new and improved GEVIs are developed, and imaging techniques become more sophisticated, we can expect even more detailed insights into the electrical dynamics of cells and circuits. This will not only advance our understanding of fundamental biological processes but also pave the way for new diagnostic and therapeutic strategies for a wide range of neurological and other disorders.
Engineering Better Voltage Sensors
Future development of genetically encoded voltage indicators is expected to build on advances in sensor design and application. The reviewed opportunities include protein-engineering strategies to improve GEVI dynamic range and kinetics. These properties are central targets for making voltage signals more useful across experiments. The review presents such engineering strategies and future opportunities as key directions for the field.