Electrophysiology

Electrophysiology (from Greek ἥλεκτ, ēlektron, "amber" [see the etymology of "electron"]; φύσις, physis, "nature, origin"; and -λογία, -logia) is the branch of physiology that studies the electrical properties of biological cells and tissues.

It involves measurements of voltage changes or electric current or manipulations on a wide variety of scales from single ion channel proteins to whole organs like the heart.

Depending on the preparation and precise placement, an extracellular configuration may pick up the activity of several nearby cells simultaneously, termed multi-unit recording.

Classical techniques allow observation of electrical activity at approximately a single point within a volume of tissue.

Interest in the spatial distribution of bioelectric activity prompted development of molecules capable of emitting light in response to their electrical or chemical environment.

After introducing one or more such compounds into tissue via perfusion, injection or gene expression, the 1 or 2-dimensional distribution of electrical activity may be observed and recorded.

To make an intracellular recording, the tip of a fine (sharp) microelectrode must be inserted inside the cell, so that the membrane potential can be measured.

In 1963, Alan Lloyd Hodgkin and Andrew Fielding Huxley won the Nobel Prize in Physiology or Medicine for their contribution to understanding the mechanisms underlying the generation of action potentials in neurons.

Their experiments involved intracellular recordings from the giant axon of Atlantic squid (Loligo pealei), and were among the first applications of the "voltage clamp" technique.

A chlorided silver wire inserted into the pipette connects the electrolyte electrically to the amplifier and signal processing circuit.

The preparation of these slices is commonly achieved with tools such as the Compresstome vibratome, ensuring optimal conditions for accurate and reliable recordings.

[5] Nevertheless, even with the highest standards of tissue handling, slice preparation induces rapid and robust phenotype changes of the brain's major immune cells, microglia, which must be taken into consideration when using this model.

Consider this example based on Ohm's law: A voltage of 10 mV is generated by passing 10 nanoamperes of current across 1 MΩ of resistance.

Patch-clamp may also be combined with RNA sequencing in a technique known as patch-seq by extracting the cellular contents following recording in order to characterize the electrophysiological properties relationship to gene expression and cell-type.

In situations where one wants to record the potential inside the cell membrane with minimal effect on the ionic constitution of the intracellular fluid a sharp electrode can be used.

These micropipettes (electrodes) are again like those for patch clamp pulled from glass capillaries, but the pore is much smaller so that there is very little ion exchange between the intracellular fluid and the electrolyte in the pipette.

The capacitive electrode (composed of the SSM and the absorbed vesicles) is so mechanically stable that solutions may be rapidly exchanged at its surface.

This property allows the application of rapid substrate/ligand concentration jumps to investigate the electrogenic activity of the protein of interest, measured via capacitive coupling between the vesicles and the electrode.

[13] The bioelectric recognition assay (BERA) is a novel method for determination of various chemical and biological molecules by measuring changes in the membrane potential of cells immobilized in a gel matrix.

BERA is the core technology behind the recently launched pan-European FOODSCAN project, about pesticide and food risk assessment in Europe.

The method has also been used for the detection of environmental toxins, such as pesticides[17][18][19] and mycotoxins[20] in food, and 2,4,6-trichloroanisole in cork and wine,[21][22] as well as the determination of very low concentrations of the superoxide anion in clinical samples.

[23][24] A BERA sensor has two parts: A recent advance is the development of a technique called molecular identification through membrane engineering (MIME).

[26] While not strictly constituting an experimental measurement, methods have been developed to examine the conductive properties of proteins and biomembranes in silico.

These are mainly molecular dynamics simulations in which a model system like a lipid bilayer is subjected to an externally applied voltage.

While atomistic simulations may access timescales close to, or into the microsecond domain, this is still several orders of magnitude lower than even the resolution of experimental methods such as patch-clamping.

For example, clinical cardiac electrophysiology is the study of the electrical properties which govern heart rhythm and activity.

Scientists such as Duchenne de Boulogne (1806–1875) and Nathaniel A. Buchwald (1924–2006) are considered to have greatly advanced the field of neurophysiology, enabling its clinical applications.

In practice a MINI module comprises a checklist of information that should be provided (for example about the protocols employed) when a data set is described for publication.