Gating (electrophysiology)
Encyclopedia
In electrophysiology
, the term gating refers to the opening (activation
) or closing (by deactivation or inactivation) of ion channels.
When ion channels are in a 'closed' (non-conducting) state, they are impermeable to ions and do not conduct electrical current. When ion channels are in an open state, they conduct electrical current by allowing some ions to pass through them, and thus across the plasma membrane
of the cell
. These flows of ions across the membrane result in an electrical current across the membrane. Gating is the process of an ion channel transforming between any of its conducting and non-conducting states.
The name 'gating' derives from the idea that an ion channel protein includes a pore that is guarded by a gate or several gates, and the gate(s) must be in the open position for any ions to pass through the pore. A variety of cellular changes can trigger gating, depending on the ion channel, including changes in voltage across the cell membrane (voltage-gated ion channel
s), drugs or hormones interacting with the ion channel (ligand-gated ion channel
s), changes in temperature , stretching or deformation of the cell membrane, addition of a phosphate
group to the ion channel (phosphorylation
), and interaction with other molecules in the cell (e.g., G protein
s). The rate at which any of these gating processes occurs in response to these triggers are known as the 'kinetics
of gating.' Some drugs and many ion channel toxins act as 'gating modifiers' of voltage-gated ion channels by changing the kinetics of gating.
The voltage-gated ion channels of the action potential
are often described as having four gating processes: activation, deactivation, inactivation, and reactivation (also called 'recovery from inactivation'). In a model of an ion channel that has two gates (an activation gate and an inactivation gate) that must both be open for ions to be conducted through the channel, 'activation' is the process of opening the activation gate, which occurs in response to the voltage inside the cell membrane (the membrane potential
) becoming more positive with respect to the outside of the cell (depolarization); 'deactivation' is the opposite process of the activation gate closing in response to the inside of the membrane becoming more negative (repolarization). 'Inactivation' is the closing of the inactivation gate; as with activation, inactivation occurs in response to the voltage inside the membrane becoming more positive, but often inactivation is found to be delayed in time compared to activation. 'Recovery from inactivation' is the opposite of inactivation. Thus, both inactivation and deactivation are processes that lead to the channel becoming non-conducting, but they are different processes in that inactivation is triggered by the inside of the membrane becoming more positive, whereas deactivation is triggered by the membrane potential becoming more negative.
Electrophysiology
Electrophysiology is the study of the electrical properties of biological cells and tissues. It involves measurements of voltage change or electric current on a wide variety of scales from single ion channel proteins to whole organs like the heart...
, the term gating refers to the opening (activation
Activation
Activation in chemical sciences generally refers to the process whereby something is prepared or excited for a subsequent reaction.- Chemistry :...
) or closing (by deactivation or inactivation) of ion channels.
When ion channels are in a 'closed' (non-conducting) state, they are impermeable to ions and do not conduct electrical current. When ion channels are in an open state, they conduct electrical current by allowing some ions to pass through them, and thus across the plasma membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
of the cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
. These flows of ions across the membrane result in an electrical current across the membrane. Gating is the process of an ion channel transforming between any of its conducting and non-conducting states.
The name 'gating' derives from the idea that an ion channel protein includes a pore that is guarded by a gate or several gates, and the gate(s) must be in the open position for any ions to pass through the pore. A variety of cellular changes can trigger gating, depending on the ion channel, including changes in voltage across the cell membrane (voltage-gated ion channel
Voltage-gated ion channel
Voltage-gated ion channels are a class of transmembrane ion channels that are activated by changes in electrical potential difference near the channel; these types of ion channels are especially critical in neurons, but are common in many types of cells....
s), drugs or hormones interacting with the ion channel (ligand-gated ion channel
Ligand-gated ion channel
Ligand-gated ion channels are one type of ionotropic receptor or channel-linked receptor. They are a group of transmembrane ion channels that are opened or closed in response to the binding of a chemical messenger , such as a neurotransmitter.The binding site of endogenous ligands on LGICs...
s), changes in temperature , stretching or deformation of the cell membrane, addition of a phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
group to the ion channel (phosphorylation
Phosphorylation
Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes....
), and interaction with other molecules in the cell (e.g., G protein
G protein
G proteins are a family of proteins involved in transmitting chemical signals outside the cell, and causing changes inside the cell. They communicate signals from many hormones, neurotransmitters, and other signaling factors. G protein-coupled receptors are transmembrane receptors...
s). The rate at which any of these gating processes occurs in response to these triggers are known as the 'kinetics
Kinetics (physics)
In physics and engineering, kinetics is a term for the branch of classical mechanics that is concerned with the relationship between the motion of bodies and its causes, namely forces and torques...
of gating.' Some drugs and many ion channel toxins act as 'gating modifiers' of voltage-gated ion channels by changing the kinetics of gating.
The voltage-gated ion channels of the action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
are often described as having four gating processes: activation, deactivation, inactivation, and reactivation (also called 'recovery from inactivation'). In a model of an ion channel that has two gates (an activation gate and an inactivation gate) that must both be open for ions to be conducted through the channel, 'activation' is the process of opening the activation gate, which occurs in response to the voltage inside the cell membrane (the membrane potential
Membrane potential
Membrane potential is the difference in electrical potential between the interior and exterior of a biological cell. All animal cells are surrounded by a plasma membrane composed of a lipid bilayer with a variety of types of proteins embedded in it...
) becoming more positive with respect to the outside of the cell (depolarization); 'deactivation' is the opposite process of the activation gate closing in response to the inside of the membrane becoming more negative (repolarization). 'Inactivation' is the closing of the inactivation gate; as with activation, inactivation occurs in response to the voltage inside the membrane becoming more positive, but often inactivation is found to be delayed in time compared to activation. 'Recovery from inactivation' is the opposite of inactivation. Thus, both inactivation and deactivation are processes that lead to the channel becoming non-conducting, but they are different processes in that inactivation is triggered by the inside of the membrane becoming more positive, whereas deactivation is triggered by the membrane potential becoming more negative.