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Upon depolarization, the four identical motifs of the sodium channel (which contain six transmembrane segments that include a pore-forming loop and a voltage sensor) move outward to allow for sodium influx. Sodium channels have the intrinsic ability to close rapidly following depolarization, and this current, named the "transient sodium current ...
Sodium channels are highly selective for the transport of ions across cell membranes. The high selectivity with respect to the sodium ion is achieved in many different ways. All involve encapsulation of the sodium ion in a cavity of specific size within a larger molecule. [3]
Voltage-gated sodium channels (VGSCs), also known as voltage-dependent sodium channels (VDSCs), are a group of voltage-gated ion channels found in the membrane of excitable cells (e.g., muscle, glial cells, neurons, etc.) with a permeability to the sodium ion Na +. They are the main channels involved in action potential of excitable cells.
Voltage-gated ion channels are often specific to ions, including Na +, K +, Ca 2+, and Cl −. Each of these ions plays an important role in the electrical behavior of the cell. [9] The gates also have unique properties with important physiological implications. For example, Na + channels open and close rapidly, while K + gates open and close ...
Ion channels may be classified by gating, i.e. what opens and closes the channels. For example, voltage-gated ion channels open or close depending on the voltage gradient across the plasma membrane, while ligand-gated ion channels open or close depending on binding of ligands to the channel. [14]
Voltage-gated ion-channels are usually ion-specific, and channels specific to sodium (Na +), potassium (K +), calcium (Ca 2+), and chloride (Cl −) ions have been identified. [1] The opening and closing of the channels are triggered by changing ion concentration, and hence charge gradient, between the sides of the cell membrane.
A positively charged region between the III and IV domains of sodium channels is thought to act in a similar way. [9] The essential region for inactivation in sodium channels is four amino acid sequence made up of isoleucine, phenylalanine, methionine and threonine (IFMT). [13] The T and F interact directly with the docking site in the channel ...
The open sodium channels allow more sodium ions to flow into the cell and resulting in further depolarisation, which will subsequently open even more sodium channels. At a certain moment this process becomes regenerative ( vicious cycle ) and results in the rapid ascending phase of action potential.