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40 Cards in this Set

  • Front
  • Back
4 types of ion channel activators
external ligand
internal ligand
voltage change
pressure / temperature
Is there more Cl inside or outside the cell
what are characteristics of the S4 family of ion channels?
the S4 family is also called the 6TMD family

these ion channels have 4 subunits/domains (I-IV), each with 6 transmembrande domains (S1-S6)

S1-S4 is the voltage sensing domain
S4 has positive residues
the P loop is between S4 and S5 and forms the channel

The S4 family includes some Na, Ca, and K channels
what is patch clamp technique?
used to study ion channels
a micropipette places a suction on a cell
tries to isolate a single ion channel
4 modes: cell attached, inside-out, outside-out, and whole-cell
the V is controlled, and the I is recorded. Now the single channel conductance can be determined at different applied voltages
what is open probability
sum of the time a channel is in the open state / the total time

this should be able to apply to a population of channels, as well
what causes the rising phase of an AP?
inward sodium current
what causes the falling phase of an AP?
outward potassium current
what causes Na channels to deactivate?
Na channels open due to depolarization. from open state there is a probability that they will go become inactivated. with time, more and more Na channels will inactivate. hyperpolarization allows them to go to resting state again
which subunits of the Na channel do what?
alpha - forms the channel/pore
beta - auxillary, modulates pore properties
how many domains do the Na channels have?
4 homologous domains, each made up of 6 transmembrane segments
what is the p loop?
in S4 family of channel, the p loop is located between the 4th and 5th transmembrane segment and forms the ion conduction pore. there are four of them, one in each homologous domain of the S4 channel
which portion of the Na channel gives it ion selectivity?
the p loop!
which part of the Na channel has basic amino acids
S4, the 4th transmembrane segment in each of the 4 subunits
what forms the VSD (voltage sensing domain) in the Na channel?
what type of channel uses a hinged lid inactivation mechanism
the Na channel
what is the inactivation gate in the Na channel?
the intracellular loop b/t homologous domain III and IV
how does the inactivation gate of the Na channel bind to the mouth of the pore?
hydrophobic interactions
what family do the voltage dependent calcium receptors belong to?
how are the voltage dependent calcium receptors different from the Na receptors
the P loop is different to have different ion selectivity

inactivation is different
which has more subunits, Na or Ca channel?
Na - alpha and beta
Ca - alpha beta and delta. once again alpha can form pore by itself. allows Ca channels to react faster or slower. more diversity among Ca channels
what is the difference between hi voltage and low voltage Ca channels?
hi voltage - need large depolarization to open
L type - long lasting, doesnt inactivate much
N type -not L and not T
P/Q, R

low voltage - need smaller voltage
T type - tiny transient, activated much earlier
where are L,N,R,P/Q,and T type Ca channels found?
L-type: Excitation-contraction coupling Calcium homeostasis Gene regulation

N, P/Q & R-types: Neurotransmitter release Dendritic Ca transients

T -type:
Repetitive firing
which type of ion channel is the most diverse?
K channels
what is the main difference b/t the 6TMD K channel and the Na and Ca channels?
instead of a big protein with 4 homologous domains, the K channel is a homotetramer.
what forms the pore in the K channel?
the P loop, just like the Na and Ca channels
what mediates the inactivation of the K channel?
the N terminal ball and chain. there are four of them in the tetramer

this is also voltage dependent inactivation
what are the 2 types of Ca dependent K channels?
SK and BK - they are like 6TMD channels but have an added S0 for a total of 7 tmd's

SK has a small conductance
BK has a big conductance

BK is gated by voltage and calcium. the calcium binds to the BK's large C terminal tail.

SK is gated by just calcium. calcium binds to its constituitively bound calmodulin.
when the intracellular calcium gets too high, it opens and the cell is hyperpolarized and made less excitable
what changes the shape and amplitude of action potentials from cell to cell?
the type and # of K channels.

for the type, the kinetics of the K channel is important.

how delayed is the K channel in opening?
when can a positive current injected into a neuron cause multiple action potentials?
when the duration of the stimulus current is longer than the Na channel refractory period
what is a burst of action potentials?
when a stimulus elicits several action potentials in a row followed by a quiet period.
What two components of a stimulus determine the frequency of the resulting AP?
the amplitude and the rate (frequency) of the stimulus
what encodes the information transmitted through nerves?
the frequency of firing.

amplitude is all or none in an action potential
how could Ia channels and Ic channels cause a difference in the frequency of AP firing?
Ia (transient K current) has fast activation. this means that the AP duration is shorter and that the inactivation of Na and K channels will be over sooner. thus the neuron will have a shorter refractory period and will be ready to fire again.

Ic is delayed rectifying K current. repolarization occurs slower. AP duration is longer. refractory period is longer. takes longer for the neuron to be ready to fire again.
Firing patterns may vary by _ and _
brain region and subcellular region
If you hyperpolarize the cell and apply a stimulus, why is there a delay in neuron firing?
The hyperpolarization will cause more of the Na channels and the Ia (transient K current) channels to be resting rather than inactivated. very few channels will be inactivated. more K channels will be available for opening upon depolarization. when the stimulus is applied, the Ia channels and Na channels will both open. However, the Ia channels will oppose the Na channels, causing difficulty in reaching threshold. it will take longer to reach threshold. This will result in a delay.
what is Im?
Im is a K channel which opens slowly but does not inactivate. This makes the cell less excitable.
What is the difference between T Type Ca channels and L type Ca channels?
T Type Ca channels open at a lower voltage. They are tiny transient. T Type channels can help the cell reach threshold to fire an AP (with opening of Na channels). this is important for bursting. inactivation of T type channels will occur after a delay.

L Type Ca channels open at a higher voltage. They are usually located in the cell body. They don't inactivate much, so they can result in a large net influx of Ca which allows Ca to accumulate during bursts of AP. Ca-dependent K channels (primarily SK) are often located nearby, and may be activated by increased Ca. This causes an outward K current resulting in afterhyperpolarization. AHP slows the firing rate of the bursting neuron by making it harder to reach threshold. When enough of the Ca dependent K channels are open, frequecy adaptation occurs, and the cell cannot generate an AP. the quiet phase of bursting results due to the AHP.
what is hyperpolarization activated ionic current?
most important in neurons which function as a pace maker, Ih is a channel which opens due to hyperpolarization and allows K and Na through. Na is facored, resulting in a reversal potential of +35 mV for the Ih channel. this results in a depolarization which can trigger an action potential.
how does a neuron pacemaker function?
1. Ih channels activated by hyperpolarization. lets Na and K pass, favors Na
2. net inward pos current
3. T type Ca channels are activated at low voltages
4. depolarizes enough to activate Na channels - depolarization.
5. burst of AP's results.
6. L type Ca channels open
7. enough Ca enters to open Kca channels.
8. outward K current slows freq of burst
9. enough Kca channels open to silence the burst. Kca channels cause an AHP.
10. AHP triggers opening of Ih channels
how might a cell turn on pacemaker activity?
turn on Ih!!