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).
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).