Guide to Electrophysiological Recording • 33
Chapter 4
very far. Tissue slices are commonly held in place in the chamber by a
weighted “net” or “grid” of fine threads.
A grid is easily made as follows. Bend a piece of 0.2-0.4 mm diameter
platinum wire into a ring small enough to fit in the bottom of your chamber,
then flatten the wire in a vise. Using a pair of fine forceps, pull a single strand
of nylon thread off a ~1 m length of unwaxed nylon dental floss. (It is very
wispy but remarkably strong.) Wrap the thread tightly in a spiral around a
strip of thin black card about 3 x 10 cm, securing each end with sticky tape.
Bending the card slightly, slip the flattened platinum ring under the threads,
and adjust its position and the spacing of the threads until the optimal grid
pattern is obtained. Finally, add a tiny spot of cyanoacrylate glue to each
thread crossing point and, after it is dry, cut the completed grid free.
Optics
Again, it is difficult to generalize about the optical requirements of the
chamber, since the optical technology in use may range from a simple
dissection scope to a multiphoton microscope. In general, however, it is
probably best to build a chamber with a glass microscope coverslip forming
the bottom, to ensure the best possible optical clarity.
Bath Electrode
The simplest kind of bath electrode is a chlorided silver wire placed in the bath
solution. However, if the chloride ion concentration of the bath is altered by
perfusion during the experiment, this kind of electrode will introduce serious
voltage offset errors. In this case it is essential to use a salt bridge for the bath
electrode. (See Chapter 5,
BATH HEADSTAGE AND ELECTRODES.) In any
case, it is good practice, at the end of every experiment, to check for drift in
electrode offsets. This is easily done by blowing out the patch and pressing
the I=0 button on The MultiClamp Commander. This will display on the
meter the pipette voltage required for zero current through the electrode. If,
for instance, the meter shows 2 mV, there has been a 2 mV drift since the
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