"Current Clamp" is a common technique in electrophysiology. This is a whole-cell current clamp recording of a neuron firing due to it being depolarized by current injection
1 Definition and scope
1.1 Classical electrophysiological techniques
1.1.1 Principal and mechanisms 1.1.2 Electrographic modalities by body part
1.2 Optical electrophysiological techniques
2 Intracellular recording
3 Extracellular recording
3.1 Single-unit recording 3.2 Multi-unit recording 3.3 Field potentials 3.4 Amperometry
4 Planar patch clamp 5 Other methods
5.1 Solid-supported membrane (SSM)-based 5.2 Bioelectric recognition assay (BERA) 5.3 Computational electrophysiology
6 Clinical reporting guidelines 7 See also 8 References 9 External links
Definition and scope
Classical electrophysiological techniques
Principal and mechanisms
simple solid conductors, such as discs and needles (singles or arrays, often insulated except for the tip), tracings on printed circuit boards, also insulated except for the tip, and hollow tubes filled with an electrolyte, such as glass pipettes filled with potassium chloride solution or another electrolyte solution.
The principal preparations include:
living organisms, excised tissue (acute or cultured), dissociated cells from excised tissue (acute or cultured), artificially grown cells or tissues, or hybrids of the above.
If an electrode is small enough (micrometers) in diameter, then the electrophysiologist may choose to insert the tip into a single cell. Such a configuration allows direct observation and recording of the intracellular electrical activity of a single cell. However, this invasive setup reduces the life of the cell and causes a leak of substances across the cell membrane. Intracellular activity may also be observed using a specially formed (hollow) glass pipette containing an electrolyte. In this technique, the microscopic pipette tip is pressed against the cell membrane, to which it tightly adheres by an interaction between glass and lipids of the cell membrane. The electrolyte within the pipette may be brought into fluid continuity with the cytoplasm by delivering a pulse of negative pressure to the pipette in order to rupture the small patch of membrane encircled by the pipette rim (whole-cell recording). Alternatively, ionic continuity may be established by "perforating" the patch by allowing exogenous pore-forming agent within the electrolyte to insert themselves into the membrane patch (perforated patch recording). Finally, the patch may be left intact (patch recording). The electrophysiologist may choose not to insert the tip into a single cell. Instead, the electrode tip may be left in continuity with the extracellular space. If the tip is small enough, such a configuration may allow indirect observation and recording of action potentials from a single cell, and is termed single-unit recording. Depending on the preparation and precise placement, an extracellular configuration may pick up the activity of several nearby cells simultaneously, and this is termed multi-unit recording. As electrode size increases, the resolving power decreases. Larger electrodes are sensitive only to the net activity of many cells, termed local field potentials. Still larger electrodes, such as uninsulated needles and surface electrodes used by clinical and surgical neurophysiologists, are sensitive only to certain types of synchronous activity within populations of cells numbering in the millions. Other classical electrophysiological techniques include single channel recording and amperometry. Electrographic modalities by body part Electrophysiological recording in general is sometimes called electrography (from electro- + -graphy, "electrical recording"), with the record thus produced being an electrogram. However, the word electrography has other senses (including electrophotography), and the specific types of electrophysiological recording are usually called by specific names, constructed on the pattern of electro- + [body part combining form] + -graphy (abbreviation ExG). Relatedly, the word electrogram (not being needed for those other senses) often carries the specific meaning of intracardiac electrogram, which is like an electrocardiogram but with some invasive leads (inside the heart) rather than only noninvasive leads (on the skin). Electrophysiological recording for clinical diagnostic purposes is included within the category of electrodiagnostic testing. The various "ExG" modes are as follows:
Modality Abbreviation Body part Common in clinical use
electrocardiography ECG or EKG heart (specifically, the cardiac muscle), with cutaneous electrodes (noninvasive) Very common
electroatriography EAG atrial cardiac muscle Uncommon
electroventriculography EVG ventricular cardiac muscle Uncommon
intracardiac electrogram EGM heart (specifically, the cardiac muscle), with intracardiac electrodes (invasive) Somewhat common
electroencephalography EEG brain (usually the cerebral cortex), with extracranial electrodes Somewhat common
electrocorticography ECoG or iEEG brain (specifically the cerebral cortex), with intracranial electrodes Somewhat common
electromyography EMG muscles throughout the body (usually skeletal, occasionally smooth) Very common
electrooculography EOG eye (entire globe) Somewhat common
electroretinography ERG retina specifically Somewhat common
electronystagmography ENG eye via the corneoretinal potential Somewhat common
electroolfactography EOG olfactory epithelium in mammals Uncommon
electroantennography EAG olfactory receptors in arthropod antennae Not applicable
electrocochleography ECOG or ECochG cochlea Somewhat common
electrogastrography EGG stomach smooth muscle Somewhat common
electrogastroenterography EGEG stomach and bowel smooth muscle Somewhat common
electroglottography EGG glottis Uncommon
electropalatography EPG palatal contact of tongue Uncommon
electroarteriography EAG arterial flow via streaming potential detected through skin Uncommon
electroblepharography EBG eyelid muscle Uncommon
electrodermography EDG skin Uncommon
electrohysterography EHG uterus Uncommon
electroneuronography ENeG or ENoG nerves Uncommon
electropneumography EPG lungs (chest movements) Uncommon
electrospinography ESG spinal cord Uncommon
electrovomerography EVG vomeronasal organ Uncommon
Optical electrophysiological techniques Optical electrophysiological techniques were created by scientists and engineers to overcome one of the main limitations of classical techniques. Classical techniques allow observation of electrical activity at approximately a single point within a volume of tissue. Essentially, classical techniques singularize a distributed phenomenon. Interest in the spatial distribution of bioelectric activity prompted development of molecules capable of emitting light in response to their electrical or chemical environment. Examples are voltage sensitive dyes and fluorescing proteins. 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.
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Intracellular recording involves measuring voltage and/or current
across the membrane of a cell. 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. Typically, the resting
membrane potential of a healthy cell will be -60 to -80 mV, and during
an action potential the membrane potential might reach +40 mV. In
Alan Lloyd Hodgkin
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 voltage clamp technique allows an experimenter to "clamp" the cell
potential at a chosen value. This makes it possible to measure how
much ionic current crosses a cell's membrane at any given voltage.
This is important because many of the ion channels in the membrane of
a neuron are voltage-gated ion channels, which open only when the
membrane voltage is within a certain range.
The cell-attached patch clamp uses a micropipette attached to the cell membrane to allow recording from a single ion channel.
Main article: Patch clamp
This technique was developed by
A schematic diagram showing a field potential recording from rat hippocampus. At the left is a schematic diagram of a presynaptic terminal and postsynaptic neuron. This is meant to represent a large population of synapses and neurons. When the synapse releases glutamate onto the postsynaptic cell, it opens ionotropic glutamate receptor channels. The net flow of current is inward, so a current sink is generated. A nearby electrode (#2) detects this as a negativity. An intracellular electrode placed inside the cell body (#1) records the change in membrane potential that the incoming current causes.
Extracellular field potentials are local current sinks or sources that are generated by the collective activity of many cells. Usually, a field potential is generated by the simultaneous activation of many neurons by synaptic transmission. The diagram to the right shows hippocampal synaptic field potentials. At the right, the lower trace shows a negative wave that corresponds to a current sink caused by positive charges entering cells through postsynaptic glutamate receptors, while the upper trace shows a positive wave that is generated by the current that leaves the cell (at the cell body) to complete the circuit. For more information, see local field potential. Amperometry Amperometry uses a carbon electrode to record changes in the chemical composition of the oxidized components of a biological solution. Oxidation and reduction is accomplished by changing the voltage at the active surface of the recording electrode in a process known as "scanning". Because certain brain chemicals lose or gain electrons at characteristic voltages, individual species can be identified. Amperometry has been used for studying exocytosis in the nervous and endocrine systems. Many monoamine neurotransmitters; e.g., norepinephrine (noradrenalin), dopamine, and serotonin (5-HT) are oxidizable. The method can also be used with cells that do not secrete oxidizable neurotransmitters by "loading" them with 5-HT or dopamine. Planar patch clamp Planar patch clamp is a novel method developed for high throughput electrophysiology. Instead of positioning a pipette on an adherent cell, cell suspension is pipetted on a chip containing a microstructured aperture.
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.
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 patch pipette
Scanning electron microscope image of a planar patch clamp chip. Both the pipette and the chip are made from borosilicate glass.
A single cell is then positioned on the hole by suction and a tight connection (Gigaseal) is formed. The planar geometry offers a variety of advantages compared to the classical experiment:
It allows for integration of microfluidics, which enables automatic
compound application for ion channel screening.
The system is accessible for optical or scanning probe techniques.
Solid-supported membrane (SSM)-based
With this electrophysiological approach, proteoliposomes, membrane
vesicles, or membrane fragments containing the channel or transporter
of interest are adsorbed to a lipid monolayer painted over a
functionalized electrode. This electrode consists of a glass support,
a chromium layer, a gold layer, and an octadecyl mercaptane monolayer.
Because the painted membrane is supported by the electrode, it is
called a solid-supported membrane. It is important to note that
mechanical perturbations, which usually destroy a biological lipid
membrane, do not influence the life-time of an SSM. 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.
Bioelectric recognition assay (BERA)
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. Apart from the increased stability of the electrode-cell
interface, immobilization preserves the viability and physiological
functions of the cells. BERA is used primarily in biosensor
applications in order to assay analytes that can interact with the
immobilized cells by changing the cell membrane potential. In this
way, when a positive sample is added to the sensor, a characteristic,
"signature-like" change in electrical potential occurs. BERA is the
core technology behind the recently launched pan-European FOODSCAN
project, about pesticide and food risk assessment in Europe. BERA
has been used for the detection of human viruses (hepatitis B and C
viruses and herpes viruses), veterinary disease agents (foot and
mouth disease virus, prions, and blue tongue virus), and plant viruses
(tobacco and cucumber viruses) in a specific, rapid (1–2
minutes), reproducible, and cost-efficient fashion. The method has
also been used for the detection of environmental toxins, such as
pesticides and mycotoxins in food, and
The consumable biorecognition elements The electronic read-out device with embedded artificial intelligence.
A recent advance is the development of a technique called molecular
identification through membrane engineering (MIME). This technique
allows for building cells with defined specificity for virtually any
molecule of interest, by embedding thousands of artificial receptors
into the cell membrane.
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. Studies using these setups have been
able to study dynamical phenomena like electroporation of
membranes and ion translocation by channels.
The benefit of such methods is the high level of detail of the active
conduction mechanism, given by the inherently high resolution and data
density that atomistic simulation affords. There are significant
drawbacks, given by the uncertainty of the legitimacy of the model and
the computational cost of modeling systems that are large enough and
over sufficient timescales to be considered reproducing the
macroscopic properties of the systems themselves. 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.[citation
Clinical reporting guidelines
Minimum Information (MI) standards or reporting guidelines specify the
minimum amount of meta data (information) and data required to meet a
specific aim or aims in a clinical study. The "Minimum Information
Clinical cardiac electrophysiology
Duchenne de Boulogne
^ Scanziani, Massimo; Häusser, Michael (2009). "
Book chapter on Planar Patch Clamp
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