NPI SEC-05LX, Operating Instructions Manual

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SEC/TEC SYSTEMS WITH VCcCC MODE
General Description
The “
V oltage C lamp c ontrolled C urrent C lamp” (VCcCC) or “slow voltage clamp“ (SLOW VC)
mode is used for performing accurate current clamp recordings in the presence of membrane
potential oscillations. The npi single and two electrode current and voltage-clamp amplifiers (npi
SEC 05X/10LX; npi TEC-05X series) have been modified in a way that slow membrane potential
oscillations are exactly controlled by the voltage-clamp module without affecting faster responses,
e.g. postsynaptic potentials (PSPs) and action potentials (APs). The response speed of the voltage-
clamp feed-back circuit has been decreased by incorporation of electronic circuits with large time
constants (1 - 10000 s). In addition, fast current stimuli (e.g. for conductance measurements) can be
applied through the current clamp input (CURRENT STIMULUS BNC connector).
Operation
The VCcCC mode is controlled through two front panel elements (located in the VC part of the
front panel): a toggle switch marked “on” / “off” and a rotary switch to set the time constants (10-
100-1000, 5000 and 10000 sec) for the low-pass filter. To start using the VCcCC mode, the
amplifier must be tuned accurately in the fast VC mode (toggle switch “off”). The holding potential
control must be set on the desired value, or a holding potential signal must be provided from an
external device (e.g. a computer). This holding potential will be the preset membrane potential for
the VCcCC mode. Under these conditions, PSPs or other changes of the membrane potential will be
voltage clamped.
If the toggle switch is set “on” the VCcCC mode is started as indicated by the red LED above the
VC LED. Depending on the preset time constant, fast changes of the membrane potential will not
be voltage clamped any more. This is a condition that corresponds to an accurate current clamp.
Fast changes of the membrane potential are monitored on the potential output, slow changes are
compensated by the VCcCC circuit.
The time constant should be selected so that the signals under investigation are not altered by the
VCcCC (please compare with current clamp recordings).
Important: The average membrane potential can be changed only through the VOLTAGE
COMMAND INPUT. If changes are required, please select a short time constant (1 or 10 s).
Note : Please don’t use DHC and VCcCC mode simultaneously!!