Biophys J. 2009 Mar 4;96(5):1803-14. PMID: 19254539
At the time this paper was being written (and even now), channelrhodopsin was growing in popularity and a number of variants were being created. Each of variant has its own properties of conductance, inactivation, recovery time, etc. In this article, they examined the kinetics of different variants of channelrhodopsin. What they showed was that the variants had, in some cases, vastly different properties. For example, some were not only permeable to sodium, which is why they are useful for depolarizing neurons, but also permeable to calcium. This is important because altering calcium homeostasis could have a number of unintended consequences on cells, up to and including death. Most importantly, they were showed that the same preparations of cells, but using different variants of channelrhodopsin, have different abilities to follow high frequency trains of photostimulation, e.g. the ChEF variant is able to respond reasonably well to photostimulation at 50Hz, while channelrhodopsin 2 and its H134R variant can not reliably perform under even 25Hz trains.
The take-home message of this paper, in my opinion, is that there are many types of channelrhodopsin available. Which one you decide to use should probably be based on a good analysis of its capabilities and whether or not they are suited for the type of experiments you will be doing, not just which version is available from your favorite distributor.
-dh
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