VA-10X User Manual
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version 7.0
page 16
Carbon fiber disk microelectrodes with small diameter (5-10 µm range) can be obtained from
npi or ALA Scientific Instruments. The electrodes are manufactured using an anodic
electrophoretic insulation method (see Schulte, A. and R. Chow, 1996, Anal. Chem. 68, 3054-
3058).
6.4.
Counter Electrode
The counter electrode used for biological measurements is typically an Ag/AgCl pellet (a
sodium-saturated calomel electrode is sometimes used). The pellet should be immersed into
the recording chamber and connected via a thin wire to the ground input of the headstage.
6.5.
Amperometric Measurements
For high time resolution measurements of transmitter release from single vesicles DC
amperometry is the appropriate approach. In this approach, the carbon-fiber electrode is
energized with a command potential that exceeds the redox potential of the transmitter being
studied. In practice, a command potential of equal to or greater than +650 mV is sufficient for
measurements of all major oxidizable transmitters that have been studied so far.
To generate a command potential for DC amperometry, there should be no control voltage at
the INPUT ÷10 mV BNC, and the INPUT ÷10 mV coupling switch should be set to “OFF”.
The 3-position command toggle switch should be set for example to the “+” position. Then,
the desired potential can be dialed in with the 10-turn potentiometer. As indicated above
+650 mV is sufficient for most measurements. The amperometric signal is diffusion based.
Thus, the distance between the carbon-fiber electrode detecting face and the cell surface must
be kept to a minimum. For maximum signal size and most rapid kinetics, try to touch the cell
membrane with the electrode.
6.6.
Cyclic Voltammetry
In order to facilitate the identification of the transmitter being released, it is possible to use
various voltage waveforms. One common approach is to apply fast voltage ramp potentials,
i.e. to perform fast cyclic voltammetry.
For this application it is necessary to connect an external voltage source to the
INPUT ÷10 mV connector (#
10
, Figure 1) at the front panel of the VA-10X. Because one has
to relate the measured current to the applied instantaneous voltage, the current and the applied
voltage should be recorded simultaneously with a data acquisition system.
