Final Exam Flashcards
How many transmembrane regions does a K ion channel need?
6 transmembrane regions
How many transmembrane regions does a Ca/Na ion channel need?
24 transmembrane regions
What are some K channel subtypes and how many transmembrane domains do they have?
Inward rectifier - 2 TMD
Two pore K - 4 TMD
What are the three families of ligand-gated ion channels?
- Cys-loop - nACh, GABA(A), glycine, 5HT and ZAC (zinc)
- Glutamate - NMDA, AMPA and kainate
- P2X
What are the stoichiometric subunits in neuronal vs muscular ACh?
Muscle – a, b, y/E, d
Neuronal
a2 – a6
b2 – b4
a7 – a10
Where is the highest concentration of voltage-gated sodium channels?
Initial segment
What produces neuron resting potential?
Sodium, potassium and chlorine leak channels
How do Na+/K+ ATPases maintain the concentration gradient through ATP hydrolysis?
3 Na+ ions out
2 K+ ions in
How does the electrochemical driving force (Vm – Eion) affect ion flux?
Negative = positive ions into the cell
Positive = negative ions into the cell
What is Ohm’s Law?
V = I x R
What is membrane capacitance?
Ability to store charge Q when a voltage difference V occurs between two surfaces
What are some features of capacitors?
Material properties – lipid bilayer
Areas of two conducting surface
–> Larger area – increases capacitance
Thickness of insulating layer
–> Greater thickness – decreases capacitance
What is the time constant equal to?
t = Rm x Cm
What is the difference between electrical and chemical synapses?
Electrical - gap junctions (hemichannels built from connexin proteins)
Chemical - neurotransmitter release and ion flow through postsynaptic channels
How does a voltage-clamp amplifier work?
Keeps the membrane potential constant by pumping current into the cell to counteract movement of current across the membrane
What experiment was conducted by Labarca et al.?
Mutations of Leucine9’ to Serine on M2 of nAChRs
Where is L9’ facing when channel is opened?
Facing away from the pore
What is the significance of mutating Leucine to Serine?
Leucine is very hydrophobic whereas serine is hydrophilic
What happened to EC50 with the Leu9’Ser mutation?
EC50 decreased 10-fold with each subunit mutation (1-4 mutations)
What was the wild type EC50 compared to the 4* mutation type?
WT = 24uM
4M* = 2.0-2.3nM
What happened to channel opening and bursting with the mutations?
Channel opened longer and bursting lasted longer
What are the effects of hydropathy on channel opening?
More hydrophobic (Leu) = harder to open
What happens when MTSEA and ACh are applied to nAChR together with a L251C mutation?
Leads to smaller response (inhibited)
What does it mean when every second residue of M2 is accessible by MTSEA?
Every second residue must face the pore, so M2 must be a beta-strand structure
What does it mean when every fourth residue of M2 is accessible by QX-222?
Every fourth residue must face the pore, so M2 must be an alpha-helix structure
Where does L251 face when the channel is open?
Faces the toward the pore (opposite of Labarca et al)
What is different about pentameric ligand-gate ion channels?
Doesn’t have a cys-loop
Where was L251 pointing in the Cyro EM structure of torpedo nAChR?
Pointed toward adjacent subunits, not towards the pore
What type of interactions was determined play a role in gating in the Cyro EM structure of torpedo nAChR?
Hydrophobic-hydrophobic interactions
What form the two hydrophobic rings that act as the effective gate of the channel in the Cyro EM structure of torpedo nAChR?
Leu9’ and Val13’
What would happen with disruption of the hydrophobic-hydrophobic interactions?
Subunits no longer interact, channel would open more easily
What does Leu9’ make side-to-side hydrophobic interaction with to produce a tight “hydrophobic girdle”?
Neighboring alanine
What happens to the conformation of M2 when it moves to the open position?
M2 straightens
