104 • Reference Section
MultiClamp 700A Theory and Operation, Copyright 2000, 2001 Axon Instruments, Inc.
Mode
• Recording mode is switchable between voltage clamp (VC), normal current clamp
(IC) and current clamp in which all external inputs are disconnected (I=0).
• Mode is selected using the
buttons, or remotely by checking the Ext
check box and applying a voltage to the MODE input on the front panel of the
MultiClamp 700A (0 V for IC, 3.5-5 V for VC).
• See also Headstage, Input/Output Connections.
Switching between V-Clamp and I-Clamp modes in the MultiClamp 700A activates a
switch between two distinct circuits in the CV-7A headstage. Voltage clamp is
achieved with a current-voltage converter, whereas current clamp is achieved with a
voltage follower. This contrasts with the design of other patch clamp amplifiers, in
which the same basic circuit is used for voltage clamp and current clamp, producing a
compromised performance.
The I=0 mode is a special case of I-Clamp in which all external inputs are
disconnected. This is convenient if you wish to quickly return to the resting potential
of the cell, or if you want to check the electrode offset at the end of the experiment.
(See Chapter 4,
GENERAL ADVICE.)
Mode switching in the MultiClamp 700A can, under some circumstances, produce a
small transient at the input of the headstage, a transient that is seen by the cell. We
have extensively tested the headstage with many cell types and all recording
configurations, and have not encountered any problems with the transients causing
damage of the cell membrane.
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