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Encyclopedia > Electrophysiology
"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
"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

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. Image File history File links Download high-resolution version (840x531, 7 KB) A whole-cell current-clamp recording I made of a Substantia Nigra Pars Reticulata neuron. ... Image File history File links Download high-resolution version (840x531, 7 KB) A whole-cell current-clamp recording I made of a Substantia Nigra Pars Reticulata neuron. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell. Cells in culture, stained for keratin (red) and DNA (green). ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... In electricity, current is the rate of flow of charges, usually through a metal wire or some other electrical conductor. ... Ion channels are pore-forming proteins that help to establish and control the small voltage gradient that exists across the plasma membrane of all living cells (see cell potential) by allowing the flow of ions down their electrochemical gradient. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... The heart and lungs, from an older edition of Grays Anatomy. ... Drawing of the cells in the chicken cerebellum by S. Ramón y Cajal Neuroscience is a field that is devoted to the scientific study of the nervous system. ... Neurons (also called nerve cells) are the primary cells of the nervous system. ... A. A schematic view of an idealized action potential illustrates its various phases as the action potential passes a point on a cell membrane. ...

Contents

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. Such a configuration allows direct observation and recording of the intracellular electrical activity of a single cell. Intracellular activity may also be observed using a specially formed (hollow) glass pipette. In this technique, the microscopic pipette tip is pressed against the cell membrane, to which it tightly adheres. The electrolyte within the pipette may be brought into fluid continuity with the cytoplasm by delivering pulse of pressure to the electrolyte 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 ion channels 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 the electrical activity of a single cell, termed single unit recording. Depending on the preparation and precise placement, an extracellular configuration may pick up simultaneously the activity of several nearby cells, termed multi-unit recording. Single unit recording refers to the use of an electrode to record the electrophysiological activity (action potentials) from a single neuron. ...


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 number in the millions. A local field potential (LFP) is a particular class of electrophysiological signals, which is related to the sum of all dendritic synaptic activity within a volume of tissue. ...


Other classical electrophysiological techniques include single channel recording and amperometry.


Optical electrophysiological techniques

Optical electrophysiological techniques were created by scientists and engineers to overcome one of the main limitations of classical techniques. Approximately, classical techniques allow observation electrical activity at 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 fluoresceing 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. (expand this section)



Many particular electrophysiological readings have specific names:

ECG may also refer to the East Coast Greenway Lead II An Electrocardiogram (ECG or EKG, abbreviated from the German Elektrokardiogramm) is a graphic produced by an electrocardiograph, which records the electrical voltage in the heart in the form of a continuous strip graph. ... The heart and lungs, from an older edition of Grays Anatomy. ... Electroencephalography is the neurophysiologic measurement of the electrical activity of the brain by recording from electrodes placed on the scalp or, in special cases, subdurally or in the cerebral cortex. ... For more specific information about the human brain, see its main article at human brain A sketch of the human brain by artist Priyan Weerappuli, imposed upon his sketch of the profile of Michaelangelos David In animals, the brain, or encephalon (Greek for in the head), is the control... Electrocorticography (ECoG) is the practice of using an electrode placed directly on the brain to record electrical activity directly from the cerebral cortex. ... Location of the cerebral cortex Slice of the cerebral cortex, ca. ... Electromyography (EMG) is a medical technique for evaluating and recording physiologic properties of muscles at rest and while contracting. ... A top-down view of skeletal muscle Muscle (from Latin musculus little mouse[1]) is contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. ... Electrooculography (EOG) is a medical technique for measuring the resting potential of the retina, the resulting signal is called electrooculogram. ... A human eye. ... Electroretinography, is used to measure the electrical responses of various cell types in the retina, including the light-sensitive cells (rods and cones) and the ganglion cells. ... Human eye cross-sectional view. ... Electroantennogram or EAG is a technique by which we measure the average output of the antenna to the brain for a given odor. ... Olfactory receptors are a type of G protein-coupled receptor in olfactory receptor neurons. ...

Intracellular recording

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 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. Today, most microelectrodes used for intracellular recording are glass micropipettes, with a tip diameter of < 1 micrometre, and a resistance of several megaohms. The micropipettes are filled with a solution that has a similar ionic composition to the intracellular fluid of the cell. A chlorided silver wire inserted in to the pipet connects the electrolyte electrically to the amplifier and signal processing circuit. The voltage measured by the electrode is compared to the voltage of a reference electrode, usually a silver-silver chloride wire in contact with the extracellular fluid around the cell. In general, the smaller the electrode tip, the higher its electrical resistance, so an electrode is a compromise between size (small enough to penetrate a single cell with minimum damage to the cell) and resistance (low enough so that small neuronal signals can be discerned from thermal noise in the electrode tip). This article or section is in need of attention from an expert on the subject. ... Alan Lloyd Hodgkin photo: taken 1963 Nobel prize photo Sir Alan Lloyd Hodgkin, OM, KBE, FRS (February 5, 1914 – December 20, 1998) was a British physiologist and biophysicist, who won the 1963 Nobel Prize in Physiology or Medicine for his work with Andrew Fielding Huxley on the basis of nerve... Sir Andrew Fielding Huxley OM FRS (born 22 November 1917, Hampstead, London, England, UK) is a British physiologist and biophysicist, who won the 1963 Nobel Prize in Physiology or Medicine for his work with Alan Lloyd Hodgkin on the basis of nerve action potentials, the electrical impulses that enable the... The squid giant axon is the very large (up to 1 mm in diameter; typically around 0. ... Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ...


Voltage clamp

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 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. Voltage clamp measurements of current are made possible by the near-simultaneous, digital subtraction of transient capacitive currents that pass as the recording electrode and cell membrane are charged to alter the cell's potential. (See main article on voltage clamp.) Image File history File links Voltage_clamp. ... Image File history File links Voltage_clamp. ... In biological cells that are electrically at rest, the cytosol possesses a uniform electric potential or voltage compared to the extracellular solution. ... Ion channels are pore-forming proteins that help to establish and control the small voltage gradient that exists across the plasma membrane of all living cells (see cell potential) by allowing the flow of ions down their electrochemical gradient. ... Voltage-gated ion channels are a class of trans-membrane ion channels that are activated by the surrounding potential difference near the channel (or near the cell, neuron or synapse). ... Electrophysiology is the science and branch of physiology that pertains to the flow of ions in biological tissues and, in particular, to the electrical recording techniques that enable the measurement of this flow. ...


"Current Clamp" describes recording the trans-membrane voltage with the ability to inject current into a cell through the recording electrode. Unlike in the voltage clamp mode, where the membrane potential is held at a level determined by the experimenter, in "current clamp" mode the membrane potential is free to vary, and the amplifier records whatever voltage the cell generates on its own or as a result of stimulation. This technique is used to study how a cell responds when electrical current enters a cell; this is important for instance for understanding how neurons respond to neurotransmitters that act by opening membrane ion channels. Chemical structure of D-Aspartic Acid, a common Amino Acid neurotransmitter. ... Ion channels are present in the membranes that surround all biological cells. ...


Most current-clamp amplifiers provide little or no amplification of the voltage changes recorded from the cell. The "amplifier" is actually an electrometer, sometimes referred to as a "unity gain amplifier"; its main job is to change the nature of small signals (in the mV range) produced by cells so that they can be accurately recorded by low-impedance electronics. The amplifier increases the current behind the signal while decreasing the resistance over which that current passes. Consider this example based on Ohm's Law: A voltage of 10 mV is generated by passing 10 nanoamperes of current across 1 of resistance. The electrometer changes this "high impedance signal" to a "low impedance signal" by using a voltage follower circuit. A voltage follower reads the voltage on the input (caused by a small current across a big resistor. It then instructs a parallel circuit that has a large current source behind it (the electrical mains) and adjusts the resistance of that parallel circuit to give the same output voltage, but across a lower resistance. An electrometer is an electrical instrument for measuring electric charge or electrical potential difference. ... Electrical impedance, or simply impedance, is a measure of opposition to a sinusoidal alternating electric current. ... The ampere (symbol: A) is the SI base unit of electrical current equal to one coulomb per second. ... The ohm (symbol: Ω) is the SI unit of electric resistance. ... A buffer amplifier (sometimes simply called a buffer) is one that provides electrical impedance transformation from one circuit to another. ... Resistor symbols (non-European) Resistor symbols (Europe, IEC) A pack of resistors A resistor is a two-terminal electrical or electronic component that resists an electric current by producing a voltage drop between its terminals in accordance with Ohms law. ...


The patch-clamp technique.

The cell-attached patch clamp uses a micropipette attached to the cell membrane to allow recording from a single ion channel.
The cell-attached patch clamp uses a micropipette attached to the cell membrane to allow recording from a single ion channel.

The patch clamp technique was developed by Erwin Neher and Bert Sakmann who received the Nobel Prize in 1991. Conventional intracellular recording involves impaling a cell with a fine electrode; patch-clamp recording takes a different approach. A patch-clamp microelectrode is a micropipette with a relatively large tip diameter. The microelectrode is placed next to a cell, and gentle suction is applied through the microelectrode to draw a piece of the cell membrane (the 'patch') into the microelectrode tip; the glass tip forms a high resistance 'seal' with the cell membrane. This configuration is the "cell-attached" mode, and it can be used for studying the activity of the ion channels that are present in the patch of membrane. If more suction is now applied, the small patch of membrane in the electrode tip can be displaced, leaving the electrode sealed to the rest of the cell. This "whole-cell" mode allows very stable intracellular recording. A disadvantage (compared to conventional intracellular recording with sharp electrodes) is that the intracellular fluid of the cell mixes with the solution inside the recording electrode, and so some important components of the intracellular fluid can be diluted. A variant of this technique, the "perforated patch" technique, tries to minimise these problems. Instead of applying suction to displace the membrane patch from the electrode tip, it is also possible to withdraw the electrode from the cell, pulling the patch of membrane away from the rest of the cell. This approach enables the membrane properties of the patch to be analysed pharmacologically. Image File history File links Patchclamp1. ... Image File history File links Patchclamp1. ... Classical patch clamp setup, with microscope, antivibration table and micro manipulators Complete miniaturized planar patch clamp setup Patch clamp technique is a technique in electrophysiology that allows the study of individual ion channels in cells. ... Classical patch clamp setup, with microscope, antivibration table and micro manipulators Complete miniaturized planar patch clamp setup Patch clamp technique is a technique in electrophysiology that allows the study of individual ion channels in cells. ... Erwin Neher (born 1944 in Landsberg am Lech, Bavaria) is a German biologist. ... Bert Sakmann (born June 12, 1942) is a German cell physiologist. ...


Sharp electrode technique

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 micropipets (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 electrlolyte in the pipete. The resistance of the electrode in 10s or 100s of in this case. Often the tip of the electrode is filled with various kinds of dyes like Lucifer yellow to fill the cells recorded from, for later confirmation of their morphology under a microscope. The dyes are injected by applying a positive or negative, DC or pulsed voltage to the electrodes depending on the polarity of the dye. The ohm (symbol: Ω) is the SI unit of electric resistance. ...


Extracellular recording

Single Unit recording

An electrode introduced into the brain of a living animal will detect electrical activity that is generated by the neurons adjacent to the electrode tip. If the electrode is a microelectrode, with a tip size of about 1 micrometre, the electrode will usually detect the activity of at most one neuron. Recording in this way is generally called "single unit" recording. The action potentials recorded are very like the action potentials that are recorded intracellularly, but the signals are very much smaller (typically about 1 mV). Most recordings of the activity of single neurons in anesthetized animals are made in this way, and all recordings of single neurons in conscious animals. Recordings of single neurons in living animals have provided important insights into how the brain processes information. For example, David Hubel and Torsten Wiesel recorded the activity of single neurons in the primary visual cortex of the anesthetized cat, and showed how single neurons in this area respond to very specific features of a visual stimulus. Hubel and Wiesel were awarded the Nobel Prize in Physiology or Medicine in 1981. If the electrode tip is slightly larger, then the electrode might record the activity generated by several neurons. This type of recording is often called "multi-unit recording", and is often used in conscious animals to record changes in the activity in a discrete brain area during normal activity. Recordings from one or more such electrodes which are closely spaced can be used to identify the number of cells around it as well as which of the spikes come from which cell. This process is called spike sorting and is suitable in areas where there are identified types of cells with well defined spike characteristics. If the electrode tip is bigger still, generally the activity of individual neurons cannot be distinguished but the electrode will still be able to record a field potential generated by the activity of many cells. David Hunter Hubel (b. ... Torsten Nils Wiesel (b. ... Brodmann area 17 (primary visual cortex) is shown in red in this image which also shows area 18 (orange) and 19 (yellow) The visual cortex refers to the primary visual cortex (also known as striate cortex or V1) and extrastriate visual cortical areas such as V2, V3, V4, and V5. ... Spike sorting is a class of techniques used in the analysis of electrophysiological data. ...


Field potentials

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.
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. Image File history File links Download high resolution version (2133x1110, 126 KB)A schematic diagram representing the recording of field potentials from a hippocampal neuron. ... Image File history File links Download high resolution version (2133x1110, 126 KB)A schematic diagram representing the recording of field potentials from a hippocampal neuron. ... In a synapse between two neurons, the cell that releases the neurotransmitter is referred to as the presynaptic cell. ... The extracellular field potential is the electrical potential produced by cells, e. ... Synapses allow nerve cells to communicate with one another through axons and dendrites, converting electrical signals into chemical ones. ... Glutamate is a neurotransmitter in nerve cells which binds to all glutamate receptors located on neuron membranes, and is an example of a transmembrane receptor. ... A local field potential (LFP) is a particular class of electrophysiological signals, which is related to the sum of all dendritic synaptic activity within a volume of tissue. ...


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 neural and endocrine systems. Many monoamine neurotransmitters, e.g., norepinephrine (noradrenalin), dopamine, 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. Neurotransmitters are chemicals that are used to relay, amplify and modulate electrical signals between a presynaptic and a postsynaptic neuron. ... Norepinephrine (INN) or noradrenaline (BAN) is a catecholamine and a phenethylamine with chemical formula C8H11NO3. ... This article or section is in need of attention from an expert on the subject. ... Serotonin (5-hydroxytryptamine, or 5-HT) is a monoamine neurotransmitter synthesized in serotonergic neurons in the central nervous system (CNS) and enterochromaffin cells in the gastrointestinal tract. ...


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.
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 than be excluded after sealing. An Antivibration table is not necessary.
In planar patch configuration the cell is positioned by suction - relative movements between cell and aperture can than 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 Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ...


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 - perfusion of the intracellular side can be performed. Ion channels are pore-forming proteins that help to establish and control the small voltage gradient that exists across the plasma membrane of all living cells (see cell potential) by allowing the flow of ions down their electrochemical gradient. ... Scanning probe microscopy (SPM) is a branch of microscopy that forms images of surfaces using a physical probe that scans the specimen. ... In cell biology, molecular biology and related fields, the word intracellular means inside the cell. It is used in contrast to extracellular (outside the cell). ...


The Bioelectric Recognition Assay (BERA)

The Bioelectric Recognition Assay (BERA) is a novel method for 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 primary used in biosensor applications in order to assay analytes which 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 has been used for the detection for human viruses (Hepatitis B and C viruses, herpes viruses) and veterinary disease agents (foot and mouth disease virus, prions, blue tongue virus) and plants (tobacco and cucumber viruses) in a highly specific, rapid (1-2 minutes), reproducible and cost-efficient fashion. The method has also been used for the detection of environmental toxins, such as herbicides and the determination of very low concentrations of superoxide anion in clinical samples. A recent advance in the evolution of the BERA technology was the development of a technique called Molecular Identification through Membrane Engineering (MIME). This technique allows for building cells with absolutely defined specificity against virtually any molecule of interest, by embedding thousand of artificial receptors into the cell membrane.


See also

A Transcutaneous Electrical Nerve Stimulator, more commonly referred to as a TENS unit and pronounced tens, is an electronic device that produces electrical signals used to stimulate nerves through unbroken skin. ...

External links for planar patch clamp

  • Device description
  • Patch Clamp on a Chip
  • Equipment*Comparison

External links

  • EP Lab Digest - Trade Publication for EP Professionals

  Results from FactBites:
 
Electrophysiology - Wikipedia, the free encyclopedia (1642 words)
Electrophysiology is the study of the electrical properties of biological cells and tissues.
It involves measurements of voltage differences across cell membrane, and studies of how the flow of electrical current across membranes is regulated.
There are two major divisions of electrophysiology: intracellular recording and extracellular recording.
Electrophysiology - definition of Electrophysiology in Encyclopedia (402 words)
Electrophysiology is the science and branch of physiology that pertains to the flow of ions in biological tissues and, in particular, to the electrical recording techniques that enable the measurement of this flow.
These include so-called passive recording as well as the "voltage clamp" and "patch clamp" techniques, which "clamp" or maintain the cell potential at a level the experimenter may specify.
Amperometry is another technique of electrophysiology, which uses a carbon electrode and is typically used to detect and record changes in the chemical composition of the biological solution being studied.
  More results at FactBites »

 
 

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