L8 Ion Channels Flashcards Preview

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Flashcards in L8 Ion Channels Deck (14):
1


What can lead to an increase in membrane capictance of sodium (gNa+)

Increasing intracellular sodium woud increase gNa+

2

What can cause a focal depolarization of the plasma
membrane?

Inward Ionic Current (+ charge moves in)

3


What is voltage clamping used for?

1. A method for measuring the “whole cell response” for a given class of ion channels.

2. A method of compensating for membrane capacitance so that membrane resistance can be directly measured in
current - voltage plots (V=IR).

4


How is Voltage Clamping done?

1. Apply a constant command
voltage (Vcom) across the plasma
membrane.

2. Record the transmembrane current
(Itm) required to sustain the constant
command voltage

5


What are the results of voltage clamping?

 

A current - voltage plot that
describes the channels under
investigation.

Slope of the curve = Gx (whole cell conductance of ion x)

6


What do the downward and upward slopes of a current response plot represent in volatge clamping of fast Na+ channels.

The downward slope is due to the opening of Na+ channels and cell depolarization (inward Ionic current), An upward slope is the result of outward current.

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7


What does voltage clamping an area with no voltage gated channels demonstrate?

Leakage Channels

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8


What is the relationship between whole cell
and single channel conductance?

Gx = Nxo * Yx

Gx = conductance of all channel in a whole cell

Nxo = # open channels for a given ion

Yx = conductance of 1 open channel for that ion

9

What is single channel recording?

 

What are alpha and beta in terms of an ion channel's state?

How is the magnitude of a single channel current determined?

Sectioning off a segment of membrane "membrane patch" to measure magnitude if current and the amount of time channels are open and closed.

alpha = rate of a channel closing if open
beta = rate of a channel opening if closed

The magnitude of the
single channel current (i)
depends on the value of
the single channel
conductance (gamma) and the
electrochemical driving
force (Vm - Ex):
i = gamma (Vm - Ex)

10


What are 5 functional characterizations of ion channel?

  1. Leakage
  2. Voltage-gated
  3. Ligand-gated
  4. Second messenger gated
  5. Mechanically gated

11


What is the proposed model for "Fast Na+ channels"
 opening and closing?

4 Motifs each containing 6 transmembrane subunits. The 4th subunit is the Activation Gate
Deactivation gate is a cytoplasmic loop between motifs 3 and 4

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12

What are the 5 "moleulcar faimilies" of ion channels and an example of each?

1. Gap Junction Channels.
2. Depolarization - activated ion channels.
3. Inward Rectifying K+ channels.
4.Pentameric Ligand - gated channels.
5. Ionotropic Glutamate Receptors.
 

13

Describe gap junction ion channels

6 Connexins make a connexon, connexons of adjacet cells unite to form a gap juntion.

Very High Conductance

14

What's an example of a ligand gated channel (the one most focused on in calss)?

How does it function?

What are some other ligand gated channels?

Acetylcholine receptor (AChR)

AChR has 5 subunits and 2 binding sites for acetyl choline. If no ACh is bound, channel is closed. If two ACh bind, channel is open, allowing ions to flow in/out.

Other ligand gated channels include ATP receptors, GABA receptors, glycine receptors and glutamate receptors (he said don't worry about the glutamate receptors)

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