114 • Reference Section
MultiClamp 700A Theory and Operation, Copyright 2000, 2001 Axon Instruments, Inc.
switch to the correct position. The data are recorded unambiguously and the correct
polarity can be determined during subsequent data analysis.
Positive Current
Current that flows out of the headstage into the electrode and out of the
electrode tip into the cell.
Positive/Negative Potential
A positive/negative voltage at the headstage input with respect to the bath
ground.
With these definitions it is easy to work out the correct polarity for every
recording configuration. For example, in the whole-cell or outside-out patch
configuration the electrode tip is on the intracellular face of the cell. Thus, a
negative potential, V
p
, at the headstage input (=electrode interior) is a negative
potential inside the cell. The cell’s membrane potential under voltage clamp is
therefore V
m
= V
in
– V
out
= V
p
– 0 = V
cmd
. Positive current flowing out of the
electrode must then flow from the inside to the outside surface of the cell,
which means that it is outward current.
Polarity Summary for Different Recording Configurations
Whole Cell/Outside-out Patch
Positive current = outward membrane current
Membrane potential = V
p
Inside-out Patch
Positive current = inward membrane current
Membrane potential = – V
p
Cell-attached Patch
Positive current = inward membrane current
Membrane potential = V
rest
– V
p
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