Download 6-2_RegulationOfIonChannel_BódisV

Regulation of ion channel
Bódis Viktor
2016. 10. 20
Ion channels are pore-forming membrane proteins whose functions include establishing a resting membrane
potential, shaping action potentials and other electrical signals by gating the flow of ions across the cell
membrane, controlling the flow of ions across secretory and epithelial cells, and regulating cell volume.
The rate of ion transport trough the channel is very high(often 10^6 ions per second or greater).Ions pass
through channels down thir electrochemical gradient and this process do not need energy, it is passiv
transport.The channel has two state:opened or closed. Ions flow through the channel or not.This fact is
proved by the patch clamp technique.The patch clamp technique is a laboratory technique in
electrophysiology that allows the study of single or multiple ion channels in cells. The ion channels open
instantaneously closed to the treshold voltage level, the ions flow across through the membrane, and
instantaneously the channels close.
There are two type of classification.We can classify by selectivity.There are selective, less-selective and
non-selective ion channel. And we can classify by gating: voltage, ligand and g-protein gated channels.
Voltage-gated ion channels are activated by changes in the electrical membrane potential near the channel.
The membrane potential alters the conformation of the channel proteins, regulating their opening and
closing. The opening and closing of the channels are triggered by changing ion concentration, and hence
charge gradient, between the sides of the cell membrane. Ball and chain inactivation is a model to explain
the fast inactivation mechanism of voltage-gated ion channels. A voltage gated ion channel can be in three
states: open, closed or inactivated. The ball enters the open channel and binds to the hydrophobic inner
vestibule at the center of the channel. The blockage causes inactivation of the channel by stopping the flow
of ions.
Ligand-gated ion channels are a group of transmembrane ion channel proteins which open to allow ions to
pass through the membrane in response to the binding of a chemical messenger (ligand), such as a
neurotransmitter. The function of such receptors located at synapses is to convert the chemical signal of
presynaptically released neurotransmitter directly and very quickly into a postsynaptic.
Each G protein is a heterotrimer of three subunits: α-, β-, and γ- subunits. The α-subunit (Gα) typically
binds the G protein to a transmembrane receptor protein. This receptor protein has a large, extracellular
binding domain which will bind its respective ligands ( neurotransmitters or hormones). Once the ligand is
bound to its receptor, a conformational change occurs. This conformational change in the G protein allows
Gα to bind GTP. This leads to yet another conformational change in the G protein, resulting in the
separation of the βγ-complex (Gβγ) from Gα. And the GTP- Gα binds to the ion channel and the channel
opens.