Reference Section
•
113
Chapter 5
Polarity Conventions
•
Current and voltage sign conventions used in the MultiClamp 700A system.
Biological Polarity Conventions
Inward Current
Current (carried by positive ions) that flows across the cell membrane, from
the outside surface to the inside surface.
Outward Current
Current that flows from the inside to the outside surface of the cell.
Membrane Potential
The potential inside the cell minus the potential outside the cell:
V
m
= V
in
– V
out
.
Depolarization
A positive shift in V
m
(
e.g.
from –60 mV to +80 mV) caused by a flow of
inward current.
Hyperpolarization
A negative shift in V
m
.
MultiClamp Polarity Conventions
The conventions described here apply to all amplifiers manufactured by Axon
Instruments.
To prevent confusion, Axon always uses current and voltage conventions based on the
instrument's perspective. That is, the current is defined with respect to the direction of
flow into or out of the headstage. Axon amplifiers do not have switches that reverse
the current or the voltage command polarities. This prevents forgetting to move the
