TEC-B-01 User Manual
____________________________________________________________________________________________________________________________
__________________________________________________________________________________
version 1.1
page 22
6. Positioning of Electrodes
The position of the electrodes plays an important role in tuning the clamp speed. The position of the
current electrode is especially crucial for homogeneous charging of the membrane capacitance, one
limiting factor of clamp speed. If the current electrode is placed just at the edge of the oocyte, i.e. with
a small penetration depth, the part of the membrane close to the electrode will be charged more quickly
than the membrane at the other side of the oocyte. Thus, the voltage controlled by the clamp is
different. This leads to a capacitive transient with a slow tail (see Figure 7, right side). Placing the
current electrode central in the oocytes i.e. with a large penetration depth, leads to a homogeneous
charging of the membrane. In this case the capacitive transient can be kept short by critical
compensating R
s
(see Figure 7, left side).
Figure 7: penetration depth of the current electrode and consequences for the clamp
Figure 8: demonstration of electrode positioning
Figure 8 shows the side view of positioning the electrodes in a sequence of microphotographs.
A
shows the tips coming from 45° from above just before touching the oocyte and
B
the electrodes in
their final position. The reconstruction in
C
gives the position relative to the center of the oocyte.
Figures are kindly provided by Nikolaus G. Greeff (Greeff, 2000).
