Guide
to
Electrophysiological
Recording
The
output
of
the
clamp
is
a
voltage
source
that
is
connected
to
CHANNEL
2.
The
voltage
‐
clamp
Gain
control
determines
the
steady
‐
state
accuracy
and
the
response
speed.
The
Gain
control
is
marked
in
units
of
V/V.
This
refers
to
how
many
volts
the
output
changes
for
each
volt
of
difference
between
V
m
(the
membrane
potential)
and
V
cmd
(the
command
potential).
For
example,
when
the
gain
is
at
a
value
of
10,000
V/V,
a
100
μ
V
difference
between
V
m
and
V
cmd
causes
the
output
to
shift
by
1
V.
If
the
resistance
of
CHANNEL
2
is
10
M
Ω
there
is
a
current
shift
of
100
nA.
Several
other
controls
affect
the
voltage
‐
clamp
response.
The
Lag
introduces
phase
lag
in
the
voltage
‐
clamp
amplifier.
The
Holding
control
shifts
the
clamped
membrane
potential.
The
Pipette
Capacitance
Neutralization
setting
of
CHANNEL
1
affects
the
voltage
‐
clamp
response.
The
Seal
Test
setting
delivers
a
voltage
pulse.
The
best
settings
of
the
voltage
‐
clamp
parameters
are
found
by
setting
up
the
best
possible
response
to
a
step
change
in
V
c
.
Usually,
the
ability
of
the
voltage
clamp
to
follow
a
step
change
in
command
is
identical
to
the
ability
of
the
voltage
clamp
to
follow
a
step
change
in
membrane
conductance
(Finkel
&
Gage,
1985).
General
Considerations
It
is
worthwhile
to
examine
the
pros
and
cons
of
the
TEVC
technique.
While
the
TEVC
technique
is
more
powerful
than
techniques
using
single
microelectrodes,
it
is
considerably
more
complicated
and
difficult
to
implement.
However,
the
extra
effort
will
be
well
rewarded.
If
you
are
unfamiliar
with
the
theory
behind
TEVC
systems
then
Taylor
(1991)
gives
a
good
general
overview
with
a
number
of
useful
references.
Finkel
and
Gage
(1985)
provides
a
more
thorough
discussion
of
the
theoretical
aspects.
99
