User
Guide
for
Axoclamp
900A
Voltage
Clamp
Problems
Some
problems
and
possible
causes
are
listed
below.
dSEVC
Symptom:
The
V
‐
Clamp
Gain
cannot
be
increased
to
the
level
appropriate
to
clamp
the
cell
even
after
adjusting
the
Pipette
Capacitance
Neutralization.
Possible
cause:
The
microelectrode
response
may
be
too
slow.
Suggestion:
Try
a
lower
resistance
microelectrode
such
as
a
patch
pipette.
TEVC
Symptom:
The
voltage
clamp
becomes
unstable
even
at
low
gains.
Oscillation
is
seen
on
the
current
trace
during
voltage
steps.
Possible
cause:
The
inter
‐
electrode
coupling
capacitance
may
be
too
high.
Suggestion:
Check
that
the
shield
between
the
microelectrodes
is
correctly
placed
and
adequately
grounded.
Symptom:
The
voltage
clamp
is
slow
to
respond.
There
may
also
be
a
DC
error.
Possible
causes:
The
voltage
‐
clamp
gain
is
too
low.
Suggestions:
Use
phase
lag
if
necessary
to
enable
the
gain
to
be
increased.
If
the
problem
is
present
even
at
maximum
clamp
gains
then
the
current
‐
passing
microelectrode
is
probably
blocked.
This
is
most
likely
to
occur
when
using
high
resistance
micropipettes.
Withdraw
the
current
‐
passing
microelectrode,
replace
it,
and
try
again.
Microelectrodes
filled
with
4
M
K
‐
acetate
or
K
‐
citrate
tend
to
pass
current
better
than
KCl
filled
electrodes.
162
