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As per few references, fastest G protein coupled reaction known is Drosophila melanogaster phototransduction which produces quantum bumps with average latency of 45 ms (and peak response around 200 ms). Another reaction is chemotaxis which is also in that order. I was wondering are there any known examples which are as fast as these responses?

P.S: Many ion channels are GPCR which triggers very fast but most of them takes long time (in order of seconds) to give peak ion concentration

P.S.S: By fastest I mean, minimum time required to give peak response after activation of receptor(s).

Update:

In abstract case, Let's say you got signal from outside at time t = 0. Now this will leads to reaction cascade which will take time 't1'. Assume output of this is opening of channel which will increase concentration of ion X. Now X will reach it's peak concentration at time t = t1 + t2. So I am looking for such reaction cascades with minimum time 't' (t1+t2).

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  • $\begingroup$ That is not the property of the receptor. There are many other factors that dictate the response time (the time required to achieve steady state). $\endgroup$
    – WYSIWYG
    Sep 14 '15 at 12:09
  • $\begingroup$ Yes. I am asking for smallest reaction times which involves GPCRs. And it need not be steady state. Peak time is not steady state. $\endgroup$
    – Dexter
    Sep 14 '15 at 12:13
  • $\begingroup$ Even peak time is a function of a lot of different parameters. Btw peak can be observed only in case of certain network architectures. A single reaction doesn't peak; you need a feedback (or some other kinds of motifs). Anyways, what do you exactly mean by reaction time? What is the reaction here. There can be several downstream effects some of which can be early while others are delayed. $\endgroup$
    – WYSIWYG
    Sep 14 '15 at 13:08
  • $\begingroup$ Why do you want to know this? A little context might make the question more answerable. $\endgroup$
    – James
    Sep 14 '15 at 13:13
  • $\begingroup$ @WYSIWYG , I think you didn't get my question (or I didn't explained properly). Let's say you got signal from outside at time t = 0. Now this will leads to reaction cascade which will take time 't1'. Assume output of this is opening of channel which will increase concentration of ion X. Now X will reach it's peak concentration at time t = t1 + t2. So I am looking for such reaction cascades with minimum time 't' (t1+t2). $\endgroup$
    – Dexter
    Sep 14 '15 at 13:21
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Mammalian rod cells, the most numerous photoreceptor cells in the retina, reach a max depolarization after a single photon stimulus at 100-120 ms, implying a time constant (1/k) of about 25 ms (see Chen et al., Nature 404:557). This is on the same order of speed as the fly eye, maybe a tad faster. Non-photoreceptor GPCRs are probably slower, but few folks have tried to measure these effects. The m1 muscarinic acetylcholine receptor catalyzes Gq activation with a time constant of about 500 ms (Mukhopadhyay and Ross PNAS 96:9539), but there may be faster ones.

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  • $\begingroup$ Drosophila photoreceptors are way faster than rod cells. Check out reference I provided in question. $\endgroup$
    – Dexter
    Oct 16 '15 at 5:28

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