User
Guide
for
Axoclamp
900A
The
following
four
procedures
to
minimize
the
effect
of
errors
introduced
by
R
b
are
listed
in
the
preferred
order
of
implementation.
Please
see
the
summary
at
the
end
of
this
section.
(1)
Minimize
R
b
Steps
should
always
be
taken
to
minimize
R
b
.
There
are
three
main
contributors
to
R
b
:
1.
The
cell
access
resistance
from
the
membrane
surface
to
the
bath.
2.
The
resistance
of
the
grounding
pellet.
3.
The
resistance
of
the
agar
bridge
(if
used).
Typical
values
of
the
access
resistance
of
a
1
mm
diameter
sphere
in
Ringer’s
solution
(such
as
an
oocyte)
are
on
the
order
of
150–200
Ω
.
This
is
a
given,
and
no
amount
of
manipulation
can
alter
this
for
a
given
set
of
experimental
conditions;
fortunately
it
is
relatively
small.
On
the
other
hand,
the
resistance
of
the
grounding
pellet
and
agar
bridge
are
larger,
but
one
can
take
precautions
to
minimize
them.
A
1
mm
diameter
Ag/AgCl
pellet
in
Ringer’s
solution
has
a
resistance
of
300–600
Ω
,
depending
on
how
much
of
the
surface
is
in
contact
with
the
saline.
The
larger
the
surface
area
in
contact
with
the
saline,
the
smaller
the
resistance.
The
resistance
of
an
agar
bridge
depends
on
the
length
and
diameter
of
the
bridge,
as
well
as
what
is
inside
(
i.e.,
Ringer’s
solution
vs.
3
M
KCl).
For
a
1
cm
long
bridge:
1
mm
diameter
2
mm
diameter
Ringer’s
10.2
k
Ω
2.6
k
Ω
3
M
KCl
510
Ω
130
Ω
Therefore,
to
minimize
R
b
,
it
would
be
best
to
eliminate
the
agar
bridge
and
ground
the
preparation
directly
with
a
Ag/AgCl
pellet.
The
pellet
should
be
as
large
as
practical,
and
the
area
of
it
in
contact
with
the
solution
should
be
maximized.
However,
if
the
bathing
solution
is
changed
during
the
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