Molecular Devices Axoclamp 900A, Руководство пользователя

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User Guide for Axoclamp 900A
Bridge Balance in the Bath
Some investigators like to set Bridge Balance in the bath, before attempting
to impale cells. This is to make it easier to see when a cell has been
penetrated.
Check the Tuning checkbox and set the parameters to –1 nA and 50 Hz.
Observe the Membrane Potential on Scaled Output. Press the
Auto Bridge
Balance
button; the fast voltage steps seen at the start and finish of the
current step should be eliminated. You may need to manually adjust the
Bridge Balance M
Ω
value for optimum balance. The M
Ω
value is the
resistance of the electrode.
Bridge Balance in the Cell
The Bridge Balance should be frequently checked when inside a cell,
because the electrode resistance can drift. While setting Bridge Balance,
Pipette Capacitance Neutralization should also be set (see
Capacitance
Neutralization
). Both settings can be monitored continuously through the
experiment by injecting a small current step near the beginning of each
data sweep.
It is recommended that Pipette Capacitance Neutralization be set at the
same time as Bridge Balance, because both the electrode capacitance and
the electrode resistance cause errors if left uncompensated. Also, it is easier
to correctly balance the bridge when electrode capacitance is minimized,
because the “break” between the rapidly decaying voltage across the
microelectrode and the slowly decaying voltage across the cell’s membrane
resistance is more distinct.
The balancing procedure is the same as in the bath, except that the trace
appears more rounded because of the time constant of the cell membrane.
Because the Tuning pulse width is typically brief compared with the
membrane time constant, the voltage response looks like a series of
ramping straight lines. To make it easier to see the fast voltage step in V
p
on
an oscilloscope, it is recommended that the scope input be AC coupled to
remove the resting membrane potential from the signal. The scope gain can
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