Flashcards in Voltage Gated Ion Channels Deck (16):
V-Gated Ion Channels are found in the excitable membranes of which four cell types?
Neurons, Skeletal Muscle Cells, Cardiac Muscle Cells, Smooth Muscle Cells.
What are the three types of Voltage Gated Ion Channels and where are they found?
Na+ Cells - Nerve Cells
K+ Cells - Nerve Cells
Ca++ Cells - Synapses, Muscles
At what potential are Na+ Channels closed?
At what potential do Na+ channels open rapidly and for how long do they remain open?
Open rapidly above -30mV
Close within 1-2 milliseconds.
How do V-gated Na+ channels work?
Depolarisation opens m-gates.
H-gates close the channel internally within 1-2 milliseconds.
M-gates change shape causing deactivation.
How do v-gated K+ ion channels work?
At -70mv K+ channels closed.
When cell depolarises to +40mV K+ channels open.
within 1-2 seconds the v-sensing m-gates close the channel again.
Describe the sub-units of V-gated ion channels.
Ion channels have 4 identical sub units arranged in a circle around a central aqueous pore.
How many alpha helixes span the membrane in each sub-unit of a voltage gated ion channel.
What is the function of the inner-most alpha helix (s2) in an ion channel.
Acts as a Voltage sensor.
What is the function of peptide loops linking the s5-s6 alpha helixes which line the ion channel?
Confer ion selectivity and provide targets for drugs.
There are intracellular, extracellular and transmembrane sites to which drugs can bind to V-gated ion channels. Give an example of each.
Intracellular - Local anaesthetics, Anti-epileptics (Phenytoin).
Extracellular - Tetrodotoxin
Transmembrane- Scorpion Toxin.
In what state do local anaesthetics cross membranes?
As active, non ionised lipid soluble molecules.
Na+ channel blocking drugs reduce excitation. Give three examples.
Cocaine - Early Local Anaesthetic.
Lignocain- Dental local anaesthetic.
Tetrodotoxin - Puffer fish neurotoxin.
Drugs that modify the gating of Na+ channels cause excitation, but may then block nerve conduction. Give two examples.
Batrachotoxin- Dart frog neurotoxin.
Veratridine - Plant neurotoxin.
What are the effects of K+ channe blocking drugs such as tetramethylammonium.
Enhance excitation, prolonging action potentials. Used as anti-arrythmia agents and vasodilators.