Guide to Electrophysiological Recording
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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
BATH HEADSTAGE AND ELECTRODES
in Chapter 5.) 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 700B 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 electrodes were nulled at
Chapter 4
