Current clamp

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And~'s picture
Current clamp

 Hi all,

I've got another naive question and want some help. I know the use of current clamp is to measure voltage changes across membranes.  Apparently the change in membrane potential is a result of the net movement of charge, so how is the voltage gonna change if the inward or outward current is clamped? thx.


hrparra's picture

I current clamp you fix the current injection through your pippette to set the cell at certain voltage but you do not clamp the ionic currents. i.e. Lets say that the RMP is around -60 mV and you inject some current (CC) to set the cell at -80. Then in any of the above cases there will be some ionic currents active and some inactive.
Hope I got your question and satisfied answer!

The FFM's picture
hrparra - What you just

hrparra - What you just described is how a volatge-clamp amplifer injects current to voltage clamp a cell.

In current clamp - If you clamp a cell membrane at a constant current,  if the resistance of the membrane changes during an event, like for instance when a group of ion channels opening and closing following stimulation by a neurotransmitter, so will the membrane voltage.

Ohms law  - V=IR

This is how you record changes in cell membrane potential and events like action potentials.

Depending on at what level you clamp the current will dictate if ions are actually flowing.  If you clamp at 0 pA then no current will flow, and you can record how stimulation effects the resting membrane potential