Front Panel
Middle Row
Command Rounding Switch
When this switch is on, the command potential is filtered with a time constant of 10 microseconds, which may improve the transient response of the patch clamp to changes in the command potential under some recording conditions.
Hold Control
A calibrated ten-turn potentiometer to set the holding potential (or current in current clamp mode). Full-scale is 200mV, and minimum is zero.
Hold Switch
A switch to select whether negative (the usual case!) or positive holding potentials are required. The centre (ext) position not only disables the potentiometer, but also enables an optional external input to allow switching between the two sources.
Junc Control
A calibrated ten-turn potentiometer to provide an additional holding potential adjustment from -200mV at its minimum setting to +200mV at its maximum setting, i.e. zero corresponds to five turns on this control.
Junc Switch
A switch to disable the junction potential potentiometer if this facility is not required. It also selects search mode, in which a feedback loop slowly adjusts the voltage clamp command potential in order to keep the average current at zero, while not affecting fast currents. This is useful when searching for a good patch.
Leak Control
A calibrated ten-turn potentiometer, active in voltage clamp mode, that subtracts a proportion of the command potential from the patch current, to allow purely resistive (leakage) currents to be removed from the current signal. It follows a conductance law, and full-scale corresponds to a leakage conductance of 1nanosiemen (1 gigohm resistance) in the patch and small cell modes, or 100 nanosiemens (10 megohms resistance) in the big cell mode.
Leak Switch
A switch to enable the leak subtraction if this facility is required.
Series Cond Control
A calibrated ten-turn potentiometer, also referred to in this manual as the GS control, for compensation of the access (series) resistance in the whole-cell voltage clamp recording modes. It follows a conductance law (i.e. reciprocal resistance), with a full-scale set by the cond range switch. Note that the setting of this control is used by both the RC and RS compensation circuits in the whole-cell (big or small) voltage clamp modes, and by the bridge circuit in the whole-cell current clamp modes. Also note that the control range is actually from 1% to 101% of full-scale, rather than from 0% to 100%, since zero conductance is not a meaningful setting. The adjustment range on the ten-turn dial is therefore from 0.1 to 10.1 turns, so that the dial readings remain correct. An output voltage proportional to the control setting (10V full scale) is available on the rear panel.
Cond Range Switch
This switch allows selection of a full-scale conductance of 100 nanosiemens, 300 nanosiemens or 1 microsiemen. Best normally left at 1 microsiemen, for compensation of access resistance’s from 100 megohms down to 1 megohm, but the other settings may give improved resolution for access resistance’s of 10 megohms or higher.
%Cap Offset Switch
A switch to shift the range of cell capacitances that can be compensated, by either 50% or 100% of the currently selected full scale value.
Cap Control
A calibrated ten-turn potentiometer, also referred to in this manual as the CM control, for compensation of the cell membrane capacitance in the whole-cell voltage clamp recording modes. When the cap range switch is set to its highest value, the full-scale capacitance is 10pF in the small cell mode and 100pF in the big cell mode. Capacitances of up to double these values can be compensated by using the cap offset facility. As with the series cond control, the actual adjustment range is from 1% to 101% of full scale, and an output voltage proportional to the control setting (10V full scale) is available on the rear panel.
Cap Range Switch
This switch allows selection of a full-scale cell capacitance of 10pF, 30pF or 100pF in the big cell voltage clamp mode. Best normally left at 100pF, but two lower settings may give improved resolution for capacitances within their range. In the small cell mode, the corresponding full-scale capacitances are only one-tenth as great, i.e. 1pF, 3pF and 10pF. The provision of the 1pF and 3pF ranges is a natural result of the system design, and their presence is no guarantee that they will allow such small capacitances to be measured with any higher resolution than in the 10pF range in practice. In all ranges, the cap offset switch can subtract either 50% or 100% of the full-scale capacitance, to allow over-range capacitances to be measured. For example, the cap offset switch can be used to shift the 100pF full-scale setting from its normal range of 1 to 101pF, to either 51-151pF at 50% offset or 101-201pF at 100% offset.
Phase Control
A single-turn control to set the switching phases of the control signals for the lock-in amplifier. The total phase shift provided by this control is adjustable from 0 to 180 degrees relative to the internal oscillator signal, and is independent of frequency. The phase relationships of the design are such that control settings of around 90 degrees should be aimed for (by selecting an appropriate oscillator frequency).
Phase Switch
A three-position switch to activate the control electronics for the lock-in amplifier when in either the on or dither positions. If the lock-in amplifier is not in use, this switch should be off, in order to prevent the unnecessary generation of the internal switching signals. In the off position, it also overrides selection of track mode by the RC enable switch. In the dither position, a 70Hz signal is generated to dither the cond control setting at this frequency. Its level can be varied by the small control on the rear panel, or if this control is switched off, an external conductance dither signal can be applied instead. If the RC enable switch is in the on position, this signal can be used to adjust the phase control manually, so as to zero the 70Hz signal appearing on the imaginary phase output. This condition ensures that the imaginary phase output corresponds as closely as possible to the capacitance signal, so that the effects of changes in the series conductance are minimised. It is also possible to apply an external capacitance dither signal if required. The optimum phase setting is affected by changes in the capacitance or conductance, so ordinarily the phase control needs to be readjusted from time to time. However, if the RC enable switch is in the track position when the phase switch is in the dither position, phase adjustments of up to 45 degrees in either direction relative to the actual phase control setting are carried out automatically, via an internal feedback loop which maintains the level of the conductance dither signal on the imaginary phase output at zero.
Blow Time
A single-turn control to set the duration of the blow pulse within the range 0.2-50msec. A logarithmic control is used, to give a pulse duration of about 5msec at its mid position.
Blow
A momentary switch that generates a 1.4V pulse at the electrode, to destroy the patch and thereby allow whole-cell recordings to be made.
