Outline

1
Outline

1. Cortex and hippocampus
2. Space clamp error and dendritic patch recordings
3. Dendritic spines and the postsynaptic density
4. Ionotropic versus metabotropic neurotransmitter
   receptors
5. Some general pharmacology
6. Thermodynamics.

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Cortex
Layer V pyramidal cells are huge cells that
receive inputs both proximally (from layer
II/III) and distally (from layer I). They
project to the thalamus.
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The Trisynaptic Hippocampal Loop
OUT
IN
4
Dendrites
Magee, 1999
Johnston et al., 1996
5
Space Constant (?)

• ? v(aRm)/(2Ri)
• a radius of cable
• If a 500 nm, Rm 100 M?cm2 and Ri 10 ?cm,
  then ? 50 µM
• is the distance along an infinite cylinder over
  which a potential decays e-fold.

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Space Clamp Error
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Dendritic Spines
Yuste and Denk, 1995
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The Postsyaptic Density
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Ionotropic Receptors
Receptor and channel form a single structure.
Kinetics of opening and closing are fast (ms
timescale).
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Metabotropic Receptors
Receptor is coupled to channels via a
G-protein. Most neurotransmitters have both
ionotropic and metabotropic receptors The
timecourse is on the order of seconds
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Pharmacology
Voltage Gated Channel Blockers Na- TTX (or
from inside the cell QX 314) K - TEA (or from
inside the cell Cs) Ca2 - Cadmium Ih (HCN) -
ZD7288
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Pharmacology
Ionotropic Receptor Antagonists AMPARs - NBQX
(also CNQX and DNQX) NMDARs - APV (also called
AP5) GABAARs - Picrotoxin, bicuculline and
gabazine Nicotinic AChRs - Curare,
bungarotoxin GlycineRs - strychnine
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Pharmacology
Metabotropic Receptor Antagonists mGluRs GABABR
s - CGP and saclofen Muscarinic AChRs - Atropine
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Equilibria Reactions
k1 k2
A ? B K (equilibrium constant) B/A k2/k1
this tells you where the equilibrium is
going to lie Rate formation of B (V)
k1A Enzyme do not change the equilibrium of a
reaction- they only reduce the energy of the
transition state
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The Enzyme-Substrate Complex
Observation by Michaelis
k3
k1 k2
E S ? ES ? E P Vmax k3Etotal
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Michaelis-Menten Kinetics
V k3ES Rate of formation of ES
k1ES Rate of breakdown of ES (k2
k3)ES The Michaelis Constant Km (k2
k3)/k1 Michaelis-Menten equation V
Vmax(S/SKm)
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Michaelis-Menten Kinetics
V Vmax(S/SKm)

1. When S ltlt Km, V is proportional to S
2. When S gtgt Km, V is independent of S at Vmax
3. When S Km, V is Vmax/2

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Competitive vs Noncompetitive inhibition
Competitive
Noncompetitive
By increasing S, I can be overcome. Thus,
Vmax remains the same. Km is shifted because I
changes the apparent affinity of S for E.
No amount of S can overcome I. Thus, Vmax is
decreased while Km is unchanged
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Cooperativity

• There are two varieties of cooperativity that
  result in non-Michaelis-Menten (sigmoidal) plots
• All or none- you have multiple binding sites
  and all of them are required for the reaction to
  proceed
• Facilitory- you have multiple binding sites and
  the binding of one site facilitates the binding
  of the next site (changes the on/off rate
  constants)

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Cooperativity
A Hill Plot is a log-log graph of the saturation
of the enzyme versus the concentration of the
substrate. The slope of the line is the hill
coefficient- it is the degree of cooperativity.
If the cooperativity is all or none, then hill
coefficient is equal to the number of substrate
molecules required for the reaction. If the
cooperativity is facilitory, then the hill
coefficient is a lower limit for the number of
molecules.