Overview
This lecture explains ligand-gated ion channels, their role in fast cellular signaling, their mechanism, and how they differ from other ion channel types.
Types of Membrane Receptors
- Major membrane receptor types: ligand-gated ion channels, G protein-coupled receptors, enzyme-linked receptors.
- Focus is on ligand-gated ion channels (also called ion channel linked receptors).
Ligand-Gated Ion Channels: Structure & Function
- Ligand-gated ion channels are transmembrane proteins that open or close in response to ligand binding.
- Commonly found in electrically excitable cells like neurons for rapid signal response.
- Channel is closed until a specific ligand binds to a complementary site ("lock and key" or "induced fit" model).
- Ligand binding causes a conformational change, opening the channel for ions to move.
- Binding occurs at an allosteric site, often away from the channel pore itself.
Mechanism & Effects
- Opening allows ions (like K⁺, Na⁺, Cl⁻, Ca²⁺) to flow through, changing the cell’s electrical properties.
- Converts an extracellular ligand signal into an intracellular electrical signal.
- Multiple channels can open simultaneously, amplifying the effect.
Binding Site Details
- The allosteric binding site is typically on the extracellular side; intracellular binding sites are rare.
- Some channels have multiple allosteric binding sites for ligands.
Comparison with Other Ion Channels
- Ligand-gated ion channels are distinct from voltage-gated channels (respond to membrane potential changes).
- They are also different from stretch-activated ion channels (respond to membrane deformation).
Key Terms & Definitions
- Ligand-gated ion channel — A transmembrane channel that opens or closes when a ligand binds to it.
- Ligand — A chemical messenger that binds to a receptor.
- Allosteric site — A binding site on a protein, separate from the active site, that regulates its function.
- Voltage-gated ion channel — Opens or closes in response to changes in membrane potential.
- Stretch-activated ion channel — Opens or closes in response to mechanical deformation of the cell membrane.
Action Items / Next Steps
- Review the differences between ligand-gated, voltage-gated, and stretch-activated ion channels.
- Consider examples of ligand-gated ion channels and their physiological roles, especially in neurons.