Breaking the Electrode

Once you have the electrode in the field, you can break it to the proper size. The voltage electrode should have an interior diameter of 3-5 microns. This is about 0.25 units in the ocular micrometer. The current electrode should have a diameter of 7-9 microns. This is about 0.50 units in the ocular micrometer

Breaking an electrode is a tricky matter. Accept the fact that you're going to fail the first five to ten times you try. But keep at it - it can be done.

Procedure:

1. Pull the electrode back so that it's at the edge of the field.

2. Using the control for the stage of the microscope, move the metal block into the field of the scope. Do this slowly and you'll see the field darken as the block comes close to and then enters the field.

3. Use the in/out micromanipulator control to bash the electrode against the metal block. This is the tricky part. The tip is so thin that it's flexible, so it bends instead of breaking if you approach the block too slowly. But if you bash it too hard, it will break back too far and the opening will be too large. Also, the tip will tend to disappear as it bends out of the plane of focus of the scope. The best way to break the tip is by using light, repetitive smashes, progressively getting harder. With practice you will get better at this. A bending electrode will look something like this:

4. After the tip breaks, move the metal block back and measure the diameter of the tip with the ocular micrometer. If it's around 0.5 units, put it in the petri dish labled "Voltage." If it's around 0.75 units, put it in the petri dish labled "Current." If it's bigger than 0.75 units, throw it out. If it's broken once but the hole is too small, it will break easily. Touch the metal block carefully and it will break back nicely until it's the correct width.

When you look a broken electrode it should look something like this:

When you've got 10 or more of each type of electrode ready, you'll be ready for a voltage clamp experiment.

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