Ion Channels and Their Functions

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Questions and Answers

What is the primary function of ion channels?

To control the flow of ions across membranes (correct)

To generate action potential in muscle cells

To synthesize proteins

To regulate gene expression

Which type of ion channel is responsible for detecting mechanical stimulation such as tension and pressure?

Ligand-gated ion channels

Voltage-gated ion channels

Mechanically-gated ion channels (correct)

Temperature-gated ion channels

What is the selectivity filter responsible for in voltage-gated ion channels?

Synthesizing proteins

Discriminating ions (correct)

Regulating gene expression

Generating action potential

Which type of ion channel is activated in response to the binding of a chemical messenger (ligand)?

Ligand-gated ion channels Signup and view all the answers

What is the role of the S4 helix in voltage-gated ion channels?

Forming the voltage-sensor domain Signup and view all the answers

What is the primary difference between voltage-gated ion channels and mechanically-gated ion channels?

The stimulus that triggers their activation Signup and view all the answers

Which type of ion channel is found in green algae and is named channelrhodopsin-1 and -2?

Light-gated ion channels Signup and view all the answers

What is the conformational change that occurs in response to the potential gradient in voltage-gated ion channels?

A change in the shape of the ion channel Signup and view all the answers

What is the result of a conformational change in the pore of a voltage-gated ion channel?

Opening of the channel pore Signup and view all the answers

What is the function of voltage-gated sodium channels?

Membrane depolarization in action potential Signup and view all the answers

What is the purpose of inactivation in voltage-gated ion channels?

To make the channel refractory to open Signup and view all the answers

What is the function of hyperpolarization-activated cyclic nucleotide-gated channels?

Pacemaking in the heart Signup and view all the answers

What is the result of a change in membrane voltage on S4 charges?

Movement of S4 charges in outward direction Signup and view all the answers

What is the function of voltage-gated calcium channels?

Linking muscle excitation with contraction as well as neuronal excitation with neurotransmitter release Signup and view all the answers

What is the transition from the inactivated state to the closed state referred to as?

Recovery from inactivation Signup and view all the answers

What is the function of voltage-sensitive proton channels?

Helping in acid extrusion from cell and phagocytosis Signup and view all the answers

What is the function of ligand-gated ion channels?

To convert presynaptic chemical signal into post-synaptic electrical signal Signup and view all the answers

What is the purpose of the repolarization phase in an action potential?

To restore the resting membrane potential Signup and view all the answers

What type of drugs are T-type channel blockers used as?

Antiepileptic and neuropathic painkiller drugs Signup and view all the answers

What opens voltage-gated sodium channels during an action potential?

The threshold potential Signup and view all the answers

What is the value of the electrochemical equilibrium for sodium during an action potential?

+61 mV Signup and view all the answers

What is the initial increase of the membrane potential to the value of the threshold potential called?

Hypopolarization Signup and view all the answers

What type of ion channels are involved in the repolarization phase of an action potential?

Voltage-gated potassium channels Signup and view all the answers

What is the role of the overshoot phase in an action potential?

To make the cell more electropositive Signup and view all the answers

What is the state in which the membrane potential is more negative than the default membrane potential during repolarization?

Hyperpolarization Signup and view all the answers

What is the mechanism of action of Lidocaine, a local anesthetic?

Sodium channel blocker Signup and view all the answers

What is the term used to describe diseases caused by disturbed function of ion channel subunits or the proteins that regulate them?

Channelopathy Signup and view all the answers

Which of the following diseases is caused by a mutation in the SCN5A gene, which encodes the cardiac sodium channel?

Brugada syndrome Signup and view all the answers

What is the pharmacological activity of Verapamil, a calcium channel blocker?

Antihypertensive Signup and view all the answers

Which of the following genes encodes the voltage-gated potassium channel?

KCNA1 Signup and view all the answers

What is the primary function of voltage-gated sodium channels?

To generate rapid membrane depolarization during an action potential Signup and view all the answers

What is the primary function of voltage-gated potassium channels?

To conduct potassium ions down their electrochemical gradient Signup and view all the answers

What is the relative permeability of voltage-gated calcium channels to calcium ions compared to sodium ions?

1000-fold greater Signup and view all the answers

What is the effect of activating L-type voltage-gated calcium channels in ventricular myocytes?

Prolonged action potential duration Signup and view all the answers

What is the distribution of P-type voltage-gated calcium channels?

Purkinje neurons in the cerebellum and cerebellar granule cells Signup and view all the answers

What is the effect of activating voltage-gated calcium channels in neurons?

Neuronal excitation Signup and view all the answers

What is the function of voltage-gated calcium channels in muscle cells?

To facilitate muscle contraction Signup and view all the answers

What is the name of the voltage-gated calcium channel blockers used as antihypertensive and antiarrhythmic drugs?

L-type channel blockers Signup and view all the answers

Study Notes

Ion Channels and Voltages

Ion Channels

Definition: Pore-forming membrane proteins associated with transport of specific ions in or out of the cell
Functions:
- Conductance of nerve impulse
- Generation of action potential
- Synaptic transmission
- Cardiac, skeletal, and smooth muscle contraction
- Controlling the flow of ions across membranes
Selectivity: Ion channel selectivity discriminates cations (Na+, K+, Ca+) from anions (Cl-), and allows selectivity among cations (Na+, K+, Ca+)
Classification can be based on:
- Type of ions for which they are permeable
- Type of stimulus that triggers their activation

Classification of Ion Channels Based on Stimulus

Voltage-gated ion channels: Open following a change in the membrane voltage potential
Ligand-gated ion channels: Allow ions to flow across the pore in response to the binding of a chemical messenger (ligand) to the cytoplasmic or extracellular side of the channel
Temperature-gated ion channels: Represented by thermo-sensitive ion channels that belong to the transient receptor potential channel family
Light-gated ion channels: Found in green algae and are named channelrhodopsin-1 and -2
Mechanically-gated ion channels: Able to detect mechanical stimulation such as tension, pressure, stretch, and cell volume change

Voltage-Gated Ion Channels

Voltage-sensitive
Conformational change occurs in response to the potential gradient
Distributed along the axon and soma of the neurons
Structure:
- Each subunit is composed of six transmembrane helices named S1-S6 flanked by intracellular N and C termini
- S1-S4 forms the voltage-sensor domain (VSD) with a positively charged S4
- S5-S6 forms the pore domain with the selectivity filter that discriminates the ions
- Four subunits tetramerize to form an ion channel with a central pore-forming unit surrounded by four VSDs
Gating dynamics:
- Can be in three states: closed, open, or inactivated
- Opening of the channel pore leads to the flow of ions according to the electrochemical gradient across the membrane
- Channels go from a closed state (non-conducting) to an open-state (permeable to ions) as a result of a conformational change in the pore
- Following activation, the channels go through an inactivated state during which the channel is non-conducting and refractory to open, so-called inactivation

Types of Voltage-Gated Ion Channels

Voltage-gated sodium channels: Responsible for membrane depolarization in action potential
Voltage-gated potassium channels: Responsible for membrane repolarization in action potential
Voltage-gated calcium channels: Play an important role in linking muscle excitation with contraction as well as neuronal excitation with neurotransmitter release
Hyperpolarization-activated cyclic nucleotide-gated channel: Pacemaking channels in the heart, sensitive to cAMP, cGMP that alter the voltage sensitivity of the channels
Voltage-sensitive proton channels: Strongly pH-regulated that helps in acid extrusion from cell and phagocytosis

Ligand-Gated Ion Channels

Definition: 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
Structure: Two domains; transmembrane domain including channel pore and extracellular domain including ligand binding site
Function: Conversion of presynaptic chemical signal into post-synaptic electrical signal to elicit a cellular response
Examples: Receptors for acetylcholine and glutamate

Biological Implication of Ion Channels

Action potential:
- Definition: Nerve signals generated and conducted by neurons to transmit to target tissues
- Phases: Hypopolarization, depolarization, overshoot, repolarization, and hyperpolarization
Therapeutic applications:
- Different medical conditions have been attributed to ion channel dysfunction
- Examples for drugs targeting ion channels: Lidocaine (sodium channel blocker) and Verapamil (calcium channel blocker)
Ion channel dysfunction and diseases:
- Channelopathies: Diseases caused by disturbed function of ion channel subunits or the proteins that regulate them
- Examples: Cystic fibrosis, Brugada syndrome, and Episodic ataxia

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Description

Test your knowledge of ion channels, including their primary function, types, and roles in detecting mechanical stimulation, responding to chemical messengers, and their structural components.