Title: Outline
1Outline
- Cortex and hippocampus
- Space clamp error and dendritic patch recordings
- Dendritic spines and the postsynaptic density
- Ionotropic versus metabotropic neurotransmitter
receptors - Some general pharmacology
- Thermodynamics.
2Cortex
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.
3The Trisynaptic Hippocampal Loop
OUT
IN
4Dendrites
Magee, 1999
Johnston et al., 1996
5Space 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.
6Space Clamp Error
7Dendritic Spines
Yuste and Denk, 1995
8The Postsyaptic Density
9Ionotropic Receptors
Receptor and channel form a single structure.
Kinetics of opening and closing are fast (ms
timescale).
10Metabotropic 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
11Pharmacology
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
12Pharmacology
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
13Pharmacology
Metabotropic Receptor Antagonists mGluRs GABABR
s - CGP and saclofen Muscarinic AChRs - Atropine
14Equilibria 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
15The Enzyme-Substrate Complex
Observation by Michaelis
k3
k1 k2
E S ? ES ? E P Vmax k3Etotal
16Michaelis-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)
17Michaelis-Menten Kinetics
V Vmax(S/SKm)
- When S ltlt Km, V is proportional to S
- When S gtgt Km, V is independent of S at Vmax
- When S Km, V is Vmax/2
18Competitive 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
19Cooperativity
- 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)
20Cooperativity
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.