Glowing channels shed light on plasticity
I’m sure Coffee Mug can explain a lot more about the significance of this, but in a new article in Science researchers report fusing a fluorescent protein to a particular potassium channel, known as Kv1.1, and using this to determine the site of synthesis of the channel. The particular type of fluorescent protein they used has one neat property that made this task a lot easier. When synthesized it has a green color, but when excited by UV light in the right way, it becomes red. Therefore, the protein made before and after this “photoconversion” process can be distinguished. It was found that the Kv1.1 that appears in the membrane in dendrites is synthesized locally, within those dendrites, rather than in the cell body. In addition, it was found that activation of the NMDA receptor dramatically decreased the rate of local synthesis of Kv1.1 This effect was found to be dependent on a protein called mTOR, which gets its name from its interaction with the drug rapamycin (which in fact is a well-known immunosuppressant, although it sounds like something you take to keep loud, rhythmic music from making you sick).
What could be the significance of this local down-regulation? Well, those of you with a background in neurophysiology will know that potassium channels hyperpolarize neurons, making them less likely to fire an action potential. Also, NMDA receptors are excitatory and seem to play a role in learning and memory. By shutting off production of potassium channels, the stimulus registered by the NMDA receptor can be reinforced, leading to potentiation of the dendrite’s response.
i just read it.. i have to think for a little while how their technique improves on FRAP (fluorescence recovery after photobleaching).. also there is an experiment where they use an NMDA receptor antagonist and it alters Kv1.1 production.. i’m not sure it goes the way it should though… i’m not sure how to predict which way it should go though because activating NMDARs can drive plasticity in the same way as deactivating them does sometimes.. (like in Sutton and Schuman’s synaptic scaling experiments..) i guess they had an AMPAR blocker there too..
anyway. the broader importance of the paper relates to the subject of this Sutton and Schuman review that came out in cell yesterday, so maybe i’ll make time to do a MEGAPOST!! on it and why local protein synthesis is important and all that.