Neuro430 Lecture

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Neuro430 Lecture 2
Announcements 1. Student Questions 2. Rector
Contact Info drector_at_vetmed.wsu.edu Office
Wegner G11 5-1587 or Lab McCoy South S115
5-8735 3. Lab Manuals 4. Gen Ed 302 Help with
Writing 5. First come basis for model ideas
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Standing Waves - ./RIP
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Cell Membrane Structure
Membranes are impermeable to most
molecules Channels Provide a pathway into
cells Can be selective Can open and close Can
allow passive transport Also provide active
transport (Pumps) Complex structure imparts
function of the channel Why is Na channel bigger
than K? Ions are hydrated (Cellular Swelling,
Imaging)
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How channels are made
1. DNA unfolding 2. RNA transcription 3.
Ribosome attachment and translation 4. Folding
and Secondary structure 5. Combination with
other subunits and tertiary structure 6.
Insertion into the membrane
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The purpose of membrane channels
1. Establish and maintain the intracellular
environment There is not much the cell can do
about it's external environment 2. Detect and
provide a response to changes in the
environment Examples Bacteria, Nitella 3.
Identify particles and provide a
response Example transmitter binding 4. Make
use of concentration gradients to do work E.g.
Nernst Equation
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Channel Types
1. Membrane Passive Ion Channels E.g. Cloride,
Water 2. Membrane Gated Ion Channels E.g.
Sodium, Potassium, Calcium 3. Gap Junctions 4.
Active Ion Pumps
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3 Models to opening and closing
Voltage Gated Na Channel
Voltage Gated K Channel
Voltage Gated Na Channel
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4 Control Mechanisms
Nicotinic Acetylcholine Receptor
Various Calcium Channels
Voltage Gated Na Channel
Skin Receptor Channels
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3 (4) Mechanisms for Inactivation
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Principles of Drug Action
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Antagonist Binding Affinity
Binds different site, changes the binding curve
for agonist
Binds Same site, changes concentration of bound
agonist
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Processes of Addiction
1. Exogenous Antagonists or Agonists bind to
Channel 2. Cells are programmed to expect a
certain amount of binding/activity 3. Excessive
Antagonist or Agonist Binding will cause the
cells to up-regulate or down-regulate the channel
population 4. Now, for the cell to receive
proper input, Exogenous Drugs must be present
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Channel Structure from Subunits
Single chain with multiple passes through the
membrane
Heterooligomers
Homooligomers
Multiple pore subunits with auxilliary subunits
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Ways to Identify Channel Structure
1. Molecular structure DNA sequence 2.
Biochemical Properties Binding actions and
locations 3. Biophysical Properties X-ray
diffraction Nuclear Magnetic Resonance Signals
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Molecular Structure
1. Amino acid sequence analsysis 2. Bind and
cleave assays can tell us which side of the
membrane the subunits on spanning 3. Amino acid
homology can be used to predict the structure of
other channels 4. Genetic mutations can also
tell us about the structure and function
Hydrophobic regions
Hydrophilic regions
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Biophysical Properties Revealed Through X-Ray
Crystallography
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Channel Families
Four Identical Subunits
Six subunit pairs, joining cells
Single chain with many membrane spanning regions
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Three Variants of the K Channel
4 repeated subunits
4 subunits, shortened
2 subunits, (joined later)
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Patch Clamp Technique
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Observe Channel Opening
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Measure Channel Resistance
Hold the membrane potential and measure the
current that flows through the channel. ERI
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Gramicidin Example
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RectifiersAllow current to flow only in one
direction
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Extracellular Ligand Gated
nACHr nicotinic acetylcholine receptor pass
all cations depolarize the cell -
excitatory GABA(A) and Glycine receptors pass
chloride channels hyperpolarize the cell
inhibitory 5-HT (Serotonin-gated) cation
selective excitatory P2X, P2X3 ATP activated
channel Na and Ca selective Glutamate NMDA,
AMPA, Kainate, GluR-B Ca, Na, or K selective
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Voltage Gated Channels
Sodium Voltage Gated Ion Channel Na
selective Potassium Voltage Gated Ion Channel K
Selective Calcium Voltage Gated Ion Channel Ca
Selective Voltage Gated Proton (H) Ion
Channel Adjusts cells pH Voltage Gated Anion
Channel Anion selective (e.g. Chloride)
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Intracellular Ligand Gated IonChannels
ATP-sensitive Potassium Channels CFTR a
Chloride Channel Calcium Activated Chloride
Channels EnaC amiloride-sensitive Sodium
Channel (kidney) Calcium Activated Potassium
Channel cGMP Channels pass Na and Ca G-Protein
Activated Inwardly Rectifying Potassium
Channel IP3 mediated Calcium Channel (Cell
death) Calcium activated Chloride
Channels Calcium Release Activated Channels GORK
delayed outwardly rectifying K
channel Aquaporins cGMP gated ion and water
channel
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Mechanosensitive Channels
Mechanosensitive Ion Channels pass water and
chlroide VRAC volume regulated anion
channel CLC group of chloride channels respond
to changes in cell volume ASICs acid sensing
ion channels selective for Na involved in
cardiac ishemia
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Miscellaneous
KCNK K selective 'leak' channels highly
regulated, but by what? GAP Junctions can pass
molecules to 1000 angstroms most cells are 200 A
apart, but with GAP junctions, 20 A Guard Cell
Slow Anion Channel Intracellular (nuclear)
Chloride Channel binds MAP kinase (regulates
cell growth) Numerous Bacterial and Viral
channels used to attack host cells Gramicidin,
Influenza M2 protein, Alpha Toxin, VPU
(AIDS), Porins