A Membrane protein that regulates the flow of ions. This is a kind of active Cell transport.
They can be open or closed and work as molecular electric nanoswitches.
A permeation theory for single-file ion channels: Concerted-association’dissociation
A permeation theory for single-file ion channels: One- and two-step models
Examples
GABA receptors
Sodium-potassium pump
Uses huge amount of ATP
Properties
Selective to particular Ions
Gating: they switch between open and close state due to certain signals:
- Ligands
- Voltage
- Mechanical signal: membrane stress, as in the sense of Touch!
Selectivity for potassium
Sodium, being smaller but with same charge has a larger electric field around it. The selectivity is due to the fact that the ions are in Water Solution (Chemistry). Potassium is easier to dehydrate as it attracts water less strongly as it's bigger.
Isoenergetic and aquomimetic diffusion pahtway..
The Carbonyl group in the Peptide bond gives the polar bond (like those in water). Their arrangement mimicks the arrangament of water molecules in the hydration shell of the selected ion!
Selectivity for sodium and calcium
Ongoing research
Voltage sensing
Positive charges (often Arginines –NH3+) in S4 subunit act as voltage sensor
Electromechanical coupling
Experimental techniques
Armstrong. Life among the axons (2007)
How good were the early predictions for the mechanics of ionic selectivity and voltage sensitivity?