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43 Cards in this Set

  • Front
  • Back
Important features of Ion Channels:
-Hydrophilic pores
-Form pores via geometric arrangement of subcomponents
How are ion channels anchored in the membrane?
Via hydrophobic bonding with neutral amino acids in the protein.
Surface density of Na channels in the nerve cell membrane:
100-600 / square um
Where are Na channels very high in density in the nerve membrane?
At nodes of Ranvier
How can the surface density of Fast Na channels be measured?
By labeling them with TTX or STX
What is the patch clamp technique used for?
Studying properties of single ion channels.
How is patch clamping done?
by labeling the channels with STX or TTX, then using a micropipette to form a 15 ohm seal with it.
What does the patch clamp method measure?
The ionic current through one single ion channel in a membrane.
What is the Cell-Attached configuration?
When the pipette makes contact with membrane and uses mild suction; does not break membrane or alter cytoplasmic contents.
What is the Whole-Cell configuration?
Strong suction applied to form a gigaseal, and RUPTURE the membrane.
What happens to the cell cytoplasm in the whole cell configuration?
Because of rupturing the membrane, the cell cytoplasm is replaced by the solution in the pipette.
Outside-out allows you to study what?
the effects on the extracellular side of the channel
Inside-out allows you to study what?
The effects on the intracellular side of the channel.
5 Things the Patch Clamp Technique tells you:
1. Channel conductance
2. Opening frequency
3. Open time duration
4. Response to antagonists and agonists
5. Effects of genetic altering
What are the characteristics of the Sodium channel behavior?
-Current amplitude is constant
-One/more channels can open simultaneously
-Conductance is constant
3 Types of stimuli than can activate ion channels:
1. Voltage
2. Messenger
3. Physical energy
How do voltage-operated channels respond to stimulus?
-Uniform conductance
-Frequency of opening proportional to the voltage stimulus
How are receptor-operated channels opened?
By an intracellular 2nd msgr cascade - usually leads to protein channel phosphorylation.
How do receptor-operated channels respond to stimulus?
Frequency of opening is mediated by concentration of agnost - but conductance is always uniform.
How do physical energy-dependent channels respond to stimlus?
Frequency of opening is mediated by INTENSITY of stimulus - but conductance is always uniform.
3 examples of physical-energy dependent channels:
-Shear stress dependent (baro)
-Pressure dependent (bl vessels)
-Light dependent (retinal)
What is the duration of channel open time determined by?
A poorly understood automatic inactivation mechanism.
3 Functional Properties regulated by spcfc polypeptide sequences of Ion Channels:
1. Pore structure/selectivity
2. Activation
3. Inactivation
What is a voltage gated K channel made of?
4 alpha subunits
What is the structure of an alpha subunit composed of?
6 S sequences - transmembrane a-helices with 20-27 lipophilic residues and 6 turns/sequence.
1 P sequence
What is S4?
The voltage sensor
What is the P region?
The loop between S5 and S6 that gives the channel its selectivity
What is S6?
The lumen - internal aspect of ion conductance.
What exactly allows the voltage gated K channel to open?
Membrane capacitative current which alters the ionic state of Lys and Arg residues in S4
Where do TTX and TEA and other inhibitors bind voltage gated channels?
At the p-region
How are K channels different from Na and Ca channels?
K is made of 4 discrete subunits
Na and Ca channels are each from one continuous polypeptide.
What is the continuous chain composing the Na channel like?
Pseudotetramer - 4 connected homologous monomer domains connected by polypeptide loops that extend into ECF and ICF.
Where are the Amino and Carboxy terminals of the Sodium channel polypeptide located?
In the cytosol
What exactly regulates channel selectivity for a specific ion?
-A ring of specific charged amino acids in the Pore (P) segment of the channel
-Ability of those charges to remove hydration waters
How are voltage-gated channels ACTIVATED?
By the movement of capacitative current that SIMULTANEOUSLY displaces several pos charges from amino acids on 4 contributing S4 sequences forming the channel.
What is the mechanism for Na channel inactivation?
Hinged lid
What is the mechanism for K channel inactivation?
Ball and chain
Where are the critical amino acids for the hinged lid in Na channels?
In the intracellular loop connecting S3 and S4
So the sodium channel is inactivated from what cellular side?
Intracellular - cytoplasmic
Where are the critical amino acids for the ball and chain inactivation model in K channels?
Near the Amino terminus
What is Depolarization blockade?
Inability to initiate an action potential if membrane is maintained in a depolarized state.
What causes Depolarization blockade?
Sodium inactivation gates remaining closed because of inactivating amino acids that remain in the inside cytoplasmic mouth of the channel!
3 Conditions that cause depolarization blockade:
1. Excess neurotransmitter
2. Local anesthetics
3. Increased acid in ECF