Lec 10 & 11 Flashcards
One of the 3 roles of K+ channels is to make the membrane potential (Vm) more _____ (positive/negative)
negative
One of the 3 roles of K+ channels (during repolarization) is to resist depolarization of the cell towards action potential threshold.
T or F?
True
One of the 3 roles of K+ channels is to speed up the rate of firing of action potentials. (encourage burst firing)
T or F?
False;
to slow the rate of firing of action potentials
What are the electrophysiological 4 major types of currents?
- delayed outward rectifiers
- transient outward rectifiers (A-type currents)
- Ca2+-activated K+ currents
- inward rectifiers
What is does “delayed” mean?
delay in activation
What does “Rectifier” mean?
current that flows better in one direction than another.
Which electrophysiological current types are voltage-gated K+ currents?
delayed outward rectifiers
and
transient outward rectifiers
(both are outward rectifiers)
Identification of the first gene for a voltage-gated K+ channel occurred through genetic analysis of what organism?
Shaker fruit fly.
The “Shaker” mutation was found in a gene coding for a voltage-gated K+ channel. This led to the discovery of a family of K+ channels called the _____ Family.
Shaker Family
The Shaker family is non-voltage gated.
T or F?
False
they are all voltage gated and delayed rectifiers
Members of the Shaker Family can display a range of inacivation properties.
T or F?
True
A-Type K+ Channels are not voltage gated.
T or F?
False: they are.
A-Type K+ channels refers to currents that are ___ (high/low) threshold. They _____ (slowly/rapidly) activate and inactivate K+ current.
low
rapidly
A-type K+ channels (like Na+ channels) are partially _______ (activated, inactivated) at the resting membrane potential (Vm).
inactivated
Like __-Type Ca2+ channels, A-Type K+ Channels activate at potentials below threshold and can regulate the rate at which a cell reaches the threshold for an action potential.
T type
A large A-Type current will ______ (increase/decrease) the interspike interval.
increase
A small A-Type current will ______ (increase/decrease) the interspike interval.
decrease
Kv-Type channel’s inactivation can depend on a sequence in the a-subunits or B subunits:
what is the a-subunit inactivating structure?
what is the B-subunit inactivating structure?
N - terminal domain ball
and
B-subunits,itself, blocks the channel.
In different Kv-type K+ channels, B-subunits can alter the inactivation rates.
T or F?
True
Some B-subunits attached to a Kv-Type channel will inactivate and some wont.
The KCNQ (or Kv7) family were originally identified because these genes are mutated in a condition known as…
*also found in neurons*
long QT syndrome
The neuronal version of KCNQ (Kv7) were discovered through sensitivity to muscarinic activation and were named __-type K+currents/channels.
M-type
Defects in M-type K+ channels in main neuronal members of the KCNQ (Kv7) Family underlie a type of familial ______ ______. (disease)
neonatal epilepsy
The Kv7 family mediate currents that are ____ (low/high) threshold, ______ (inactivating, non-inactivating), and very ____ (fast/slow).
low threshold
non-inactivating
very slow
A member fo the Kv7 family can contribute to the _______ (depolarization/repolarization) of the cardiac action potential because the action potential in cardiac muscle is also very ____ (slow/fast).
repolarization
slow
Activation of M-type K+ channels tends to _____ (inhibit/activate) firing over a long time scale.
inhibit
The loss of M-type currents tends to neuronal ________ (hypoexcitabiility/hyperexcitability).
hyperexcitability
without M-type there would be repetitive firing.
The two main families of Ca2+ activated K+ channels are:
large conductance (BK) channels
and
small conductance (SK) channels
Large conductance (BK) K+ channels are sensitive to what stimulus?
voltage
and
Ca2+
Small conductance (SK) channels are sensitive to what stimulus?
only to Ca2+
SK K+ channels increase their open probability (Po) in response to membrane depolarization.
T or F?
False
BK channels increase Po in response to depolarization.
What is defined as “the accumulation of Ca2+ in a cell during the firing of multiple action potentials can lead to a progressively larger Ca2+ activated K+ current, which can turn off cell firing and causing this event” ?
spike frequency adaptation
What is the name of the current that accumulates as a result of spike frequency adaptation (SFA) ?
slow afterhyperpolarization sAHP
What substance blocks Ca2+ entry and blocks sAHP slow afterhyperpolarization ?
Cd2+ cadmium ions
An increase in Ca2+ levels can cause Ca2+ activated K+ channels to burst fire.
T or F?
True
BK large conductance Ca2+ activated K+ channels have 6 transmembrane proteins.
T or F?
False;
7
Inwardly rectifying K+ channels have only 2 transmembrane spanning regions and therefore must possess the voltage-sensing S4 region.
T or F?
False;
Inwardly rectifying K+ channels have only 2 transmembrane spanning regions and therefore DO NOT possess the voltage-sensing S4 region.
Measurements of current through single Kir (inwardly rectifying) channels show that there is more likely to be current at ________ (negative/positive) voltages.
negative!
What family or type of K+ channel requires the presence of Mg2+?
Kir or inward rectifying K+ channels
Kir-type K+ channels have a voltage dependent block .
T or F?
True
Mg2+ does it.
In Kir-type channels , the current is greater on which side of the cell?
inside or outside?
inside
- due to Mg2+ on the inside , there is no current on the outside
In Kir channels, Mg2+ occludes the channel pore and prevents the exit of K+. This prevents the entrance and exit of K+ ions temporarily.
T or F?
False;
K+ ions can still enter the cell by displacing Mg2+
Inwardly rectifying K+ channels do not carry outward current.
T or F?
False;
Outward current tends to maintain a low membrane potential acting like leak channels
By increasing or decreasing the activity of the Kir channel currents, they can therefore change the membrane potential to make the cell more or less likely to fire action potentials.
What type of channel is an example of this?
ATP - sensitive (KATP ) channel
An example of a Kir channel that can be modulated is…
ATP-sensitive channel (KATP)
KATP -type Inward rectifying channels are closed by ______ (increases/decreases) in the ATP/ADP ratio which regulates insulin release in a glucose-dependent manner.
increases
therefore by increasing the amount of ATP in the cell, you will close the channels.
What type of K+ channel is glucose dependent?
KATP inwardly rectifying
What drug is used to enhance insulin release by blocking KATP channels through an action on a SUR receptor?
Sulfonlyureas
What class of drug is used in the treatment of type II diabetes?
Sulfonlyureas
What type of Ca2+ channels are important in the delivering of Ca2+ to the cell and causing the release of insulin to the body?
N and P|Q type channels
Inwardly Rectifying K+ Channels:
are selective for K+ and therefore tend to __________(depolarize, hyperpolarize) the cell and make it less likely to fire an action potential.
hyperpolarize
Inwardly Rectifying K+ Channels:
are gated
T or F?
False not gated
Inwardly Rectifying K+ Channels:
Cell voltage is never below Ek, and these channels function to allow flow of K+ ions out of the cell. much like a leak channel.
T or F?
True
Inwardly Rectifying K+ Channels:
Since they are not gated, they contribute to rapidly raising the resting membrane potential.
T or F?
False;
contribute to setting the resting membrane potential.
What are 2 examples of modulated Inward rectifying K+ channels?
GIRK channels
KATP channels
GIRK and KATP channels cause cahgnes in resting membrane potential and therefore change the excitability of the cell.
T or F?
True
exciteability = liklihood of firing action potentials.
Sulfonylurea drugs are used in maintaining blood pressure and act by blocking KATP channels, which increases the excitability of the Beta cells, leading to an increase in insultin release.
T or F?
False
used in treatment of type 2 diabetes
What family is comprised of a tandem pore or two pore K+ channel (K2P) ?
TWIK family
Which family includes tandem pores and mediates “leak” K+ currents in many types of cells?
TWIK family
Are the TWIK family of K+ channels gated?
no
A mutation in one type of two pore K+ channel (TRESK) has been linked to a familial type of ________.
migraine headache.
