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