Use of voltage clamp fluorimetry in understanding potassium channel gating: a review of Shaker fluorescence data

Voltage clamp fluorimetry (VCF) utilizes fluorescent probes that covalently bind to cysteine residues introduced into proteins and emit light as a function of their environment. Measurement of this emitted light during membrane depolarization reveals changes in the emission level as the environment of the labelled residue changes. This allows for the correlation of channel gating events with movement of specific protein moieties, at nanosecond time resolution. Since the pioneering use of this technique to investigate Shaker potassium channel activation movements, VCF has become an invaluable technique used to understand ion channel gating. This review summarizes the theory and some of the data on the application of the VCF technique. Although its usage has expanded beyond voltage-gated potassium channels and VCF is now used in a number of other voltage- and ligand-gated channels, we will focus on studies conducted in Shaker potassium channels, and what they have told us about channel activation and inactivation gating.