CSB332H1 Lecture Notes - Lecture 2: Voltage Clamp, Glass Electrode, Resting Potential
14 May 2018
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Lecture 2(b): Electrophysiology
Electrophysiology:
• Use of electrodes to measure the difference in charge:
o One reference electrode in the extracellular medium (extracellular space/fluid)
o One reference that is associated with the cell (inside or on the cell membrane)
§ Must be able to measure it against something
Voltage Clamp Technique:
• Capable of holding a membrane at a particular voltage “clamp it” using a negative feedback
o As a result are capable of observing what ions are flowing through
ð Advantage:
o This technique allows you to measure the amount of ionic current crossing a cell’s
membrane at any given voltage at a given time
Patch Clamp:
• Glass pipette can be used with any cell we suspect to find an ion channel
o Bring the glass electrode and make physical contact with the cell membrane
§ Can be used to measure the flow of ions through a
SINGLE ion channel
• Gigaohm seal is a high resistance seal ensures
that currents from through the amplifier rather
than escaping through the rim of the patch
Example:
• Visualize a neuron under a microscope, and will use a micromanipulator to allow us to move
the glass pipette into physical contact with the membrane of the neuron
o Once physical contact occurs with the membrane we will have a mild suction to allow
the pulling of the membrane into the pipette tip
§ Gigaohm seal will be formed; nothing can get through the membrane and
pipette, the only way ions can only pass is through the channel
ð When both electrodes (recording & bath electrodes) are outside the cell, no electrical
potential difference is recorded
o As soon as one electrode is inserted into the cell, the oscilloscope displays a steady
deflection of -65 mV; resting membrane potential
