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アンプ Dagan IX2-700のPDF 取扱説明書をオンラインで閲覧またはダウンロードできます。Dagan IX2-700 14 ページ。 Dual intracellular preamplifier

IX2-700 Dual Intracellular Preamplifier

Apply a train of current pulses to the electrode. Note that the Z test may not

be used for this as it disables the Bridge Balance control. This can either be from

an external source or from the Step Current Command. You will see a train of

pulses on the voltage trace of the oscilloscope. These pulses are due to the voltage

drop across the series resistance of the microelectrode. Rotate the bridge balance

control clockwise until the pulses on the amplifier output reach a minimum

amplitude. Rotation past the null point will reverse the polarity of the displayed

pulses. Adjust the bridge balance for the best null. The bridge is now balanced and

a stimulus from any source will give minimum voltage at the amplifier output. The

resistance of the electrode can be read on the ten turn dial. The bridge balance may

be locked into this position if desired.

An alternative method of balancing the bridge is as follows: Zero the voltage

trace using the offset control and note the position. Set the holding current to some

value other than zero and switch to either the + or - position. The oscilloscope trace

will depart from its previous position. Adjust the bridge balance control until the

scope trace returns to its initial position. Switch to the opposite polarity and

readjust the bridge balance. When the trace does not move when you switch

polarity, the bridge is balanced.

The main disadvantage with a bridge circuit arises from changes in the

microelectrode resistance. The circuit works on the assumption that the bridge is

balanced for the electrode resistance. Often the resistance of the electrode changes

slightly as you penetrate the cell. In some applications this will not be significant,

while in others it will. One method to attempt to correct for this change is to

balance the bridge after you have penetrated the cell. This method takes advantage

of the time it takes to charge the membrane capacitance. If the pulse duration used

to balance the bridge is sufficiently short, the potential drop recorded will be

predominantly result of the drop across the electrode. However, this does not

account for the local potential that is developed within the cell in the region of the

electrode. For a more complete discussion of this phenomena, see Peskoff and

Eisenberg (1973). Allowing for this generalization, the bridge can be balanced

within the cell (as above), but with very short pulses. Ideally these would be in the

nanosecond range, but 1 msec will usually work. Because both methods (inside

and outside cell) involve approximations, it is a good idea to try balancing the

bridge both ways to see if the results are similar. Another good routine practice is

to check the electrode resistance immediately upon leaving the cell to compare the

values. Data obtained when there is a large discrepancy between these values

should be discarded, as the true membrane potential will be unknown.