Hi!
I am working with the Axoclamp 2B Amplifier from Axon Instr.
Since I have little experience with this amplifier i am still engaged with some questions:
There are two different modes to do current clamp recordings
(A) Bridge mode
( Discontinuous Current Clamp (DCC) mode
Even though i spend quiet a while reading the manual, i am still not sure in some points.
For example: What are the advantages / disadvantages of these two modes (when compared with each other)? When (in which experimantal situation) shall one prefer working in DCC mode compared to Bridge mode and vice versa?

Any explanations or comments are appreciated.
Cheers,
Tom

sorry can't help you

Helllo Tom.
The two different modes only have one aim which is ensuring an exact measurement of the membrane potential. The bridge mode substracts the electrode potential from the entire potential ( electrode potential+cell potential ). This is because the resistance of the membrane and the resistance of the electrodes form a voltage divider. So the voltage at the electrode decays faster than the voltage of the membrane. The measuremt without compensation makes you record both potentials.
The discontinuous current clamp technique normally uses the capacitance compensation which compensates the capacitance of the electrode. As a result the voltage doesn´t decay exponential anymore but follows the current step. This is because you deleted capactive elements of the electrode and left resistance elements.
As a result both modes try to make the measurement of the membrane potential more exact. My experiences with the dcc technique make me believe that the use of the capacitance compensation is not so trivial as everybody says because when you apply a square pulse current to the electrode to adjust the capacitance (which is essential) you have to realize that the picture you see on the oscillograph is a mean value because the pictures come up to the screen with the frequency of the switching frequency (5 to 10kHz) which is much too fast for our eyes. Although you compensate precise by adjusting the voltage rectangular the measuremt can be wrong because of the mean value. The only chance to avoid this is using a computer for the representing of the electrode potential with a higher frequency to make the adjusting more precise. With this method you can make sure that you measure the membrane potential and not the electrode potential.
The bridge is usually not used in the dcc. The advantage of the bridge is that it is more robust to fluctuations although both modes can be slightly incorrect.
Using the dcc mode is wise when you want to make resistance measurements of the cell because you can inject current without any problems. Otherwise I´d use the normal mode.
Hope this helps
Katrin

A book which includes a lot of hints is the Axon Guide which you can download in the internet. Just google "Axon guide" and you´ll find it.
Best regards
Katrin

http://www.axon.com/mr_Axon_Guide.html