MT - Ion Channels Flashcards
The thalamocortical neuron has similar channel properties to the ______ in the ______.
Sa node (funny current) channels in the heart.
How many proteins are required to make a voltage-gated K+ channel? How many transmembrane domains do each of these proteins have?
Need 4 proteins, each with 6 transmembrane domains.
How many proteins are required to make an inward rectifier K+ channel? How many transmembrane domains do each of these proteins have?
Need 4 proteins, each with 2 transmembrane domains and a pore loop..
How many proteins are required to make a two pore K+ channel? How many transmembrane domains do each of these proteins have?
Need 2 proteins, each of which have 4 transmembrane domains and 2 pore loops.
Imagine a single protein from a K+ channel. Which transmembrane domain contains the voltage-sensor? What amino acids are common here.
S4. Contains many arginine residues.
Where in the body are GIRK channels found? What kind of channel are they?
They are inward rectifier K+ channels found in the heart.
What differentiates the membrane potential trace of a voltage-gated K+ channel from that of an inward rectifier K+ channel?
Vgated: rapid peak with relatively fast repolarization.
Rectifier: Slower activation but little/no repolarization.
What are the BK, IK, and SK channels (think about a specific ion/ions)?
Big (BK), intermediate (IK, and small (SK) conductance Ca2+-activated K+ channel
What toxin is capable of blocking big conductance Ca2+-activated K+ channels (BKs)(KCa1.x)?
Scorpion toxins charybdotoxin and iberiotoxin.
What channels are Scorpion toxins charybdotoxin and iberiotoxin known to block?
Big conductance Ca2+-activated K+ channels (BKs).
What toxin is capable of blocking small conductance Ca2+-activated K+ channels (SKs)(KCa2.x)?
Apamin, a component of bee venom.
What toxin is capable of blocking intermediate conductance Ca2+-activated K+ channels (IKs)(KCa3.1)?
Scorpion charybdotoxin.
How many transmembrane domains do big conductance Ca2+-activated K+ channels (BKs) have? Any pore loops?
7 (one extra!). 1 pore loop.
How many transmembrane domains do small/intermediate conductance Ca2+-activated K+ channels (SKs/IKs) have?
- 1 pore loop.
Why do bee stings hurt?
Bee venom contains aptamin. This blocks the Ca2+-activated K+ channels from repolarizing the membranes, causing perpetuated firing.
What is the K+ channel “signature sequence”? Where is it in the channel?
TVGYG. It is contained in the selectivity filter.
Each subunit in a K+ channel has _ transmembrane ______, a _______, a pore helix, and a _______ ________.
… 2 transmembrane α-helices, a turret, a pore helix, and a selectivity filter.
Are both openings of the K+ channel the same charge? What charge(s) are they?
They are both negatively charged.
How many possible locations could we find a K+ ion in the K+ channel selectivity filter?
There are 4 potential locations.
How many K+ ions are likely passing through the K+ channel filter selectivity at a given time? What else is in the channel during this time?
Only 2. 2 water molecules occupy the other 2 potential locations.
What feature of the K+ channel pore helices helps to stabilize the hydrated K+ through the channel?
They all point with their carboxyl ends towards the central cavity. This partial negative charge interacts with the cation.
How do the subunits move to open/close the K+ channel? When does this happen?
With membrane depolarization, the S4-S5 linker moves upward (closed) or downward (open), twisting the channel proteins closed/open.
How are the structures of the Na+ and Ca2+ channels similar to the K+ channels? How are they different?
They have the same general structure with 6 transmembrane domains, but instead of having these on 4 different proteins they just have one long protein with 4 of these “K+-like” 6 domain motifs. (24 TM domains total).
What toxin is known to block Na+ channels? What else?
Tetrodotoxin from pufferfish. Also lidocaine (local anesthetic) as well as phenytoin and carbamazapine (anticonvulsants).
