Ion channels

1. Ion-channels;
By
Dr. Harinatha Reddy A
ASSISTANT PROFESSOR
Department of Biotechnology
Christ University
Bangalore

2. Introduction:
 Ion channels are membrane proteins that allow ions to pass
through the Ion (channel) pore.
Their functions include establishing a
 Resting Membrane Potential,
 Action Potentials
 Other Electrical Signals by regulating the flow of ions across the
cell membrane.

3.  Ions transport through channels is extremely rapid.
 More than a million ions per second flow through open channels-
a flow rate approximately a thousand times greater than the
rate of transport by carrier proteins.

4.  Most ion channels are highly selective in allowing only one
particular type of ion to pass through the pore.
 Most of the ion channels that have been identified can exist in
either an open or a closed conformation; such channels are said
to be gated.

5.  The Important Gated ion channels are:
 Ligand-gated channels
 Voltage-gated channels
 Ligand-gated channels open in response to the binding of
neurotransmitters or other signaling molecules.
 Voltage-gated channels open in response to changes in electric
potential across the plasma membrane.

6. Na+
Acetylcholine
neurotransmitter
Ligand-gated channels:
Post synaptic
neuron
Pre synaptic neuron

7. Ligand-gated channels:
 Ligand-gated ion channels (Protein pores), also commonly referred
as ionotropic receptors, are a group of transmembrane ion-channel
proteins.
 Which open to allow ions such as Na+, K+, Ca2+, and Cl− to pass
through the membrane in response to the binding of a chemical
messenger (i.e. a ligand), such as a neurotransmitter.
 The fundamental role of ion channels in the transmission of
electric impulses.

10.  Neurotransmitters released from presynaptic cells bind to
receptors on the membranes of postsynaptic cells, where they act
to open ligand-gated ion channels.
 Binding of acetylcholine opens a channel that is permeable to
both Na+.

 This permits the rapid influx of Na+, which depolarizes the
plasma membrane and triggers an action potential.

11.  Due to influx of Na+ ions the fluid become more positive inside
of the cell these leads to depolarization of the plasma membrane.

12.  Depolarization of the plasma membrane allows action potentials
to travel down the length of nerve cell axons as electric signals,
 Resulting in the rapid transmission of nerve impulses over long
distances.
 The arrival of action potentials at the terminus of neurons release
of neurotransmitters, such as acetylcholine, which carry signals
between synapse and cells.


13. Voltage-gated ion channel:

14.  Voltage-gated ion channels are a class of transmembrane proteins
that are activated by changes in the electrical membrane potential
near the channel.
 The membrane potential alters the conformation changes of the
Ion channels, regulating their opening and closing.

15.  Voltage-gated ion-channels found along the length of the axon and
muscles tissues.
 Voltage-gated ion-channels are permeable to sodium (Na+),
potassium (K+), calcium (Ca2+), and chloride (Cl–) ions have been
identified.

16. Different types of Voltage gated Channels:
 Sodium (Na+) channels
 Calcium (Ca2+) channels
 Potassium (K+) channels
 Chloride (Cl−) channels

17. Voltage-gated ion channels in Axon:
Step:1
Step:2
axons

18. Step:3
Step:4

19. For example:
 Voltage-gated ion-channels actively pumped out Na+ ions from the
cell and pumps K+ ions into cells.
 Therefore, in the axon the concentration of Na+ is about 10 times
higher in extracellular fluids than inside the cell.
 Whereas the concentration of K+ is approximately 20 times higher
in the cytosol than in the surrounding medium.

20.  Their transport results in the establishment of an electric potential
(gradient) across the plasma membrane.
 In resting axons there is an electric potential of about - 60 mV
across the plasma membrane, with the inside of the cell negative
with respect to the outside.
 The flow of K+ through these channels makes the major
contribution to the resting membrane potential of -60 m V, which is
therefore close to the K+ equilibrium potential.

21.  Binding of neurotransmitter results allows Na+ to flow into the
cell.
 The sudden entry of Na+ leads to a large change in membrane
potential, which increases to nearly +30 m V.
 At this time, the Na+ channels are inactivated and voltage-gated
K+ channels open, substantially increasing the permeability of the
membrane to K+.

22.  K+ then flows rapidly out of the cell, driven by both the
membrane potential and the K+ concentration gradient, leading to
a rapid decrease in membrane potential to about - 75 mV.
 This change in membrane potential inactivates the voltage-gated
K+ channels and the membrane potential returns to its resting
level of -60 m V.
 .

23.  Depolarization of adjacent regions of the plasma membrane
allows action potentials to travel down the length of nerve cell
axons as electric signals.
 Resulting in the rapid transmission of nerve impulses over long
distances