Overview of a Photoswitch Optical Assay
Traditionally in optical assays ion channels have been activated by chemical perturbation, such as raising the external potassium concentration, or by field stimulation. The introduction of a light-activated channel, such as channelrhodopsin-2, makes it possible to initiate membrane depolarization with a light pulse.
The need for speed
Shown is an experiment in which patch clamp data and fluorescence data from PhoS-VSD were collected simultaneously in a HEK cell line expressing the human Nav1.7 ion channel as well as the optically-activated channelrhodopsin 2. Blue light was used to initiate an action potential by activating the channelrhodopsin which causes the membrane to depolarize. Once a threshold hold voltage is achived, the Nav1.7 sodium channels open accelerating the depolarization. The PhoS-VSD-1 dye is excited with red light (660 nm) making it ideal for use with the channelrhodopsin actuator. Note that the electrophysiological signal measured by patch clamp is identical in temporal resolution to the fluorescence signal measured with PhoS-VSD
iPSC cardiomyocytes
The Photoswitch BOLT is ideal for assaying the electrical properties of induced pluripotent stem cell (iPSC) cardiomyocytes in either a spontaneously active or optically paced condition. Shown in the figure are spontaneous action potientials from CDI iCells. The upper trace is an untreated well. The compound E4031 is a well characterized blocker of the hERG potassium channel. Increasing concentrations of E4031 produce a concentration-dependent lengthening of the action potential.
Making an information rich assay simple to execute
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