Lecture 1 Flashcards
What dictates current flow through a channel?
When open, ions flow to generate a current. When close, ions are unable to flow therefore no current is generated
How are ion channels specified?
- Molecular structure- use BLAST to see if they share similar structures to other known ion channels
- Gating- how they are gated and which molecule does this
- Regulation e.g. G protein, ATP
What is the main function of ion channels?
Allow movement of ions through IC and EC towards that ions Nernst potential which assumes that there is no net flow of ions.
What is the Nernst equation?
61.5/ 2 x log (out/in)
What is an inaccurate way of determining what type of ion channels are open?
Can compare the ion channels’ Nernst equations to the membrane potential- if numbers are similar or close it means that that particular channel is open
How does the Vm effect the Eion?
As you change the Vm, the Eion changes as the driving force for that ion changes
How do you measure total current by channels and what determines this?
I= N x g x P0 (vm-Ei)
P0 can be affected by phosphorylation, calcium or g proteins that effect activation or inhibition of the channel
N can be affected by shuttling of the channel on the membrane
How can you identify which channel types are mediating current of the cell?
Perform a whole patch clamp test to a specific potential and measure the current, then use specific channel blockers e.g. barium for potassium. If the current drops to 0 it means that the potassium channels where open and driving the membrane potential.
What are the properties of Na+ channel activation and inactivation?
Are closed at low potentials and quickly activate in high potentials. Inactivation is slower due to ball chain mechanism. They are inhibited by TTX.
What are the symptoms of FHEIG?
- Bi-temporal narrowing
- Thin upper lip
- Overgrowth of mouth tissues
- Hypertrichosis= excess body hair
- Delayed intellectual and motor skills
- Seizures and ECG abnormalities
What is the cause of FHEIG?
Mutation in KCNK4 (one aa) which is a potassium channel in PNS and CNS. Gain of function mutation which creates excess currents so Ek is less negative and there is more EC K+ which effects neighbouring neurons. Vm is closer to threshold resulting in inappropriate firing (causes seizures)
