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35 Cards in this Set

  • Front
  • Back
4 types of gating mechanisms for ion channels
external ligands
internal ligands
membrane potential
characteristics of the S4 family of ion channels
4 homologous subunits/domains
each subunit has 6 transmembrane segments
S1-S4 transmembrane domains are Voltage Sensing Domains
S4 has pos residues
what is single channel conducance
the conductance which a single open channel permits. can be determined w/ patch clamp.

often, the single channel conductance is constant
how is open probability calculated
time open / total time
when do Na channels start to inactivate?
as soon as the membrane depolarizes and they open. it is only a matter of time
what is macroscopic current?
the sum of single channel currents
what subunits make up the Na channel
alpha is the pore forming subunit. can form a pore by itself.
beta subunits are auxillary subunits that modulate the Na channel
what forms the ion conduction pore of a subunit channel?
the p loop, which dips down into the membrane but does not cross. it is located b/t the 5th and 6th TMD in each homologous subunit
what makes up the inactivation gate and its receptor in a Na channel?
the intracellular hinged lid located b/t subunit III and IV. the hydrophobic part of the mouth of the pore is the inactivation gate receptor
does inactivation of the Na channel involve the intracellular loop b/t III and IV or S4?
intracellular loop b/t III and IV

S4 plays a role in opening, but no role in inactivation
what are the subtypes of Ca channels?
L type - long lasting, takes a greater depolarization to open, dont inactivate much
excitation contraction coupling in muscle
calcium homeostasis
gene regulation
N, P/Q, R type - NT release
dendritic Ca currents
T type - opens w/ less of a depolarization. can help to depolarize enough to open Na channels and cause a depolarization
repetitive firing (used in bursting!)
what is the main difference b/t a Na channel and a Ca channel
the P loop which forms the ion conducting channel and confers ion selectivity
what kinds of subunits to Ca channels have?
more than Na
alpha - pore forming
beta, gamma, delta - auxillary, modulate alpha's function. allow for diversity
how is K channel family different from Na and Ca channel families?
much greater diversity
many different combinations of subunit #s and domains
why is the K channel gene so much shorter than Na and Ca genes?
K channel is a homotetramer, whereas Na and Ca channel are one big protein w/ 4 homologous subunits
what forms the ion conduction channel in a 6tmd K channel
the P loop b/t tmd's 5 and 6
what mediates inactivation of the K channel
the N terminal ball and chain of each K channel subunit
what are the 2 types of Ca gated K channels and what different roles do they play?
BK - big K - more similar to 6TMD channels (has 6 + S0) - big conductance - gated by Ca and Voltage - either can increase its open probability

SK - small K - small conductance - gated only by Ca - has a constituitively bound calmodulin - primarily responsible for afterhyperpolarization, frequency adaptation, the transition from a burst to quiescence
The frequency of neuronal output encodes the ____ and ___ of stimulation
rate and intensity
the diversity in firing patterns of neurons comes mainly from ____ channels
K and Ca
firing frequency is affected by the types of ___ channels in neurons
K. how long the K channel sstay open determines how fast the cell can fire the next AP (refractory period)
if you hyperpolarize the cell and then apply a stimulus, why is there a delay in firing?
hyperpolarizing the cell causes more Na and K channels to go from inactivated to resting

When the stimulus comes, the IA (transient K current) channels interfere with depolarization, causing a delay.

basically the transient K current dominates the Na current

basically the hyperpolarization removes IA inactivation, resulting in a delay
what controls IA inactivation
IA inactivation is voltage dependent. it is enhanced by depolarization and removed by hyperpolarization.

this is the reason for hyperpolarization before stimulus being able to cause a delay in the AP
transient K current vs delayed K current
transient K current (IA)
-fast activation
-Na channels quickly restored to resting state from inactivation
-AP is short, and neuron is ready to fire again very soon

delayed K current (IDR or IC)
-delayed opening
-much slower rate of repolarization
-inactivated Na channels do not return to resting as quickly
-wide AP
-neuron not ready to fire again as quickly
what is IM?
IM is a K channel which opens slowly but does not inactivate. it makes the cell less excitable by maintaining the membrane potential close to the reversal potential for K (-98)

IM is very long lasting
___ channels are involved in spike generation in neurons
__ channels are involved in frequency adaptation in neurons
Ca channels and Ca-gated K channels
which takes a higher voltage to open, L or T Ca channels?
L channels
__ channels facilitate depolarization in bursting
T type Ca channels
__ channels will result in accumulation of Ca w/in the cell
the long lasting L type Ca channels
what is frequency adaptation
when a neuron fires a lot in a short amount of time, L type Ca channels can open, and the Ca level w/in the cell can increase. this can activate Ca-gated K channels (predominantly SK), resulting in an afterhyperpolarization. thus the neuron moves from the bursting phase to the quiet phase
why would slight depolarization shift a neuron from a bursting pattern to a tonic pattern?
the T-type Ca channels that are required for bursting become inactivated with the depolarization (eg -80 -> -60)
what is IH?
Hyperpolarization-activated current. when the cell becomes hyperpolarized, this channel opens. it is permeable to both Na and K, but it favors K. This current has a reversal potential of +35 due to the favoring of Na. This channel is involved in rhythmic activity / pacemaking activity. It may be turned on and off.
what is the reversal potential of the IH current?
+35 (Na and K, favors Na)
how does pacemaking activity occur
hyperpolarization activated IH
IH slowly depolarizes the cell
T type Ca channels open, and this continues the depolarization
Na channel threshold is reached, and a burst of APs results
enough depolarization has occured to activate L type calcium channels
intracellular Ca increases and calcium-gated K channels open
the K current stops the train of APs and causes an afterhyperpolarization