User
Guide
for
Axoclamp
900A
How
to
Use
Lag
Lag
can
be
used
during
voltage
clamp
to
compensate
for
the
frequency
characteristics
of
membranes
that
are
not
well
modeled
by
a
parallel
resistance
and
capacitance.
Both
the
membrane
voltage
and
current
step
responses
should
be
improved
by
using
the
Lag.
If
only
the
membrane
voltage
step
response
is
improved
it
is
likely
that
there
is
a
resistance
(R
s
)
in
series
with
the
membrane.
In
some
cases
using
some
lag
reduces
the
current
noise
during
voltage
clamp.
See
the
discussions
on
each
type
of
voltage
‐
clamp
mode
for
more
details.
DC
Restore
One
potential
source
of
a
small
but
variable
input
leakage
current
is
due
to
DC
current
flow
through
the
dielectric
of
the
capacitor
(C )
used
for
pipette
capacitance
neutralization.
For
example,
the
pipette
potential
might
be
200
mV
(although
the
experimenter
does
not
see
this
potential
because
of
pipette
offset
compensation).
To
compensate
several
microfarads
of
input
capacitance,
the
gain
of
the
pipette
capacitance
neutralization
might
be
2.
Thus
400
mV
would
be
fed
back
to
C ,
resulting
in
200
mV
across
this
capacitor.
If
the
dielectric
resistance
of
C
were
10e
ohms,
there
would
be
2
pA
through
this
capacitor.
n
n
n
11
To
eliminate
this
source
of
leakage
current,
the
DC
Restore
circuit
removes
the
DC
voltage
from
across
C .
There
may
be
a
transient
shift
in
the
electrode
voltage
while
the
pipette
capacitance
neutralization
is
being
adjusted.
n
160
