IPSC- frequency and amplitude

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potential
potential's picture
IPSC- frequency and amplitude

Hi everyone,

Sorry for asking this kind of question. Why  frequency increase of IPSC is related with a presynaptic effect? and why amplitude increase of IPSC is related with a postsynaptic effect?

Can someone please suggest some good review articles to get me started?

Thank you very much

patchclamper
patchclamper's picture
I am not an expert on this,

I am not an expert on this, try to explain:

Increasing/decreasing in frequence means whatever happened altered the release probability of the presynaptic terminal through mechansims that change the Ca2+ concentration or vesicle release machinary. (increasing extracellular Ca2+ level, drug targeting SNARE proteins...)

Amplitude change is not necessarily all related to postsynaptic effects, for example, if receptors  are being inserted or internalized (like AMPARs in LTP/LTD), with same quantal content in a vesicle, a quantal release will cause a bigger or a smaller mIPSCs. same with block the postsynaptic receptors by an antagonist, these are the postsynaptic effects. On the other hand, if a drug is targeting VGAT, or some other way to change the vesicle refilling process, an increase or decrease of mIPSC could be a presynaptic effect due to changing of the quantal content.

Hope that helps.

potential
potential's picture
Thank you very much!

Thank you very much!

jilli
jilli's picture
Evoked and spontaneous

Evoked and spontaneous (without TTX) IPSCs are usually much greater than miniature (with TTX in bath). So an increase in amplitude in IPSC is not always a post synaptic effect. 

Whole cell current = (Number of channels)  (probability of opening of channel) (single channel conductane through an open pore)

I = N . po . i

single channel conductance through an open gaba pore is certainly post synaptic. Also number of channels is post synaptic but probability of opening also depends upon how much GABA is released (presynaptic).