Electrophysiology

Electrophysiology is the study of the electrical properties of biological cells and tissues. It involves measurements of voltage change or electrical current flow on a wide variety of scales from single ion channel proteins, to whole tissues like the heart. In neuroscience, it includes measurements of the electrical activity of neurons, and particularly action potential activity.

Definition and scope

Classical electrophysiologic techniques

Classical electrophysiology involves placing electrodes into various preparations of biologic tissue. The principle types of electrodes are: 1) simple solid conductors, such as discs and needles (singles or arrays), 2) tracings on a printed circuit boards, and 3) hollow tubes filled with an electrolyte, such as glass pippettes. The principal preparations include 1) living organisms, 2) excised tissue (acute or cultured), 3) dissociated cells from excised tissue (acute or cultured), 4) artificially grown cells or tissues, or 5) hybrids of the above.

If an electrode is small enough in diameter (on the order of microns), then the electrophysiologist may choose to insert the tip into a single cell.

Many particular electrophysiological readings have specific names:

Electrocardiography - for the heart
Electroencephalography - for the brain
Electrocorticography - from the cerebral cortex
Electromyography - for the muscles
Electrooculography - for the eyes
Electroretinography - for the retina
Electroantennography - for the olfactory receptors in arthropods

Electrophysiology Media

"Current Clamp" is a common technique in electrophysiology. This is a whole-cell current clamp recording of a neuron firing due to its being depolarized by current injection
The voltage clamp uses a negative feedback mechanism. The membrane potential amplifier measures membrane voltage and sends output to the feedback amplifier. The feedback amplifier subtracts the membrane voltage from the command voltage, which it receives from the signal generator. This signal is amplified and returned into the cell via the recording electrode.
The cell-attached patch clamp uses a micropipette attached to the cell membrane to allow recording from a single ion channel.
Schematic drawing of the classical patch clamp configuration. The patch pipette is moved to the cell using a micromanipulator under optical control. Relative movements between the pipette and the cell have to be avoided in order to keep the cell-pipette connection intact.
Scanning electron microscope image of a patch pipette.
In planar patch configuration, the cell is positioned by suction. Relative movements between cell and aperture can then be excluded after sealing. An antivibration table is not necessary.
Scanning electron microscope image of a planar patch clamp chip. Both the pipette and the chip are made from borosilicate glass.

Other websites

EP Lab Digest - Trade Publication for EP Professionals Archived 2006-05-10 at the Wayback Machine