Ion channels are important drug targets because of their critical role in nerve, cardiac, endocrine and skeletal muscle tissues. Voltage Sensor Probes (VSP) measure changes in cellular membrane electrical potential by fluorescence resonance energy transfer (FRET). It is based on a coumarin-phospholipid as a donor fluorophore that is steadily bound to the exterior membrane. The oxonol-based acceptor fluorophore associates with the exterior or interior of the membrane dependent on the membrane potential. Only if the acceptor is bound to the exterior, i.e. in resting cells with a negative potential, FRET occurs leading to a high signal.
The Omega microplate reader measured the signal of the voltage sensor probes in response to BaCl2, an inactivator of potassium ion channels. The possibility to simultaneously detect acceptor and donor fluorescence and to inject stimulants makes the Omega an ideal device to detect fast reaction by ion channels.