Why IPSCs are negative currents?

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Lostbrain
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Why IPSCs are negative currents?

Yes, why?
I got this stupid question coming to my mind today, afer a few years doing electrophysiology, but I really cannot get a clear answer. Inhibitory currents should be hyperpolarising, therefore positive. Any idea?

vilsy
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 Inhibitory currents can have

 Inhibitory currents can have both positive and negative value. It is a function of the cell membrane potential. If the cell is above the reversal potential then inhibitory currents are positive however, if below the reversal potential then they are negative. As chloride will flow in opposite directions changing the sign and the amplitude of the response. 

This is wht i think should be the reason. If i am wrong, please do let me know.

Lostbrain
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Thanks Vilsy

Thanks Vilsy

Actually, thinking about what you said, I got the answer: the reason why IPSCs are negative is that IPSCs currents are normally chloride, so that, as this ion is negative, the currents are expected to be opposite sign (this is the point I just forgot!). Therefore, IPSCs are negative but hyperpolarising.

I don't think the reversal potential has much to do with this. Inhibitory currents, by definition should go against Na channels activation, and therefore should be hyperpolarising. Another thing is that chloride can be depolarising (depending on the ECl-, but then ICl- would be depolarising, and therefore they would be considered as EPSCs. This happens in many neurons, specially during early development.

Best, and thanks again.