1 Bi/CNS 150 Lecture 5 Wednesday, October 9, 2013 Revised after lecture 10/9/13 Presynaptic transmitter release Henry Lester’s “office” hours Mon, 1:15-2 PM, Fri 1:15-2 outside the Red Door s 9, 12 (co-written by T. Sudhof, one of this week’s Nobel Prize aw
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Bi/CNS 150 Lecture 5 Wednesday, October 9, 2013 Revised after lecture 10/9/13
Henry Lester’s “office” hours Mon, 1:15-2 PM, Fri 1:15-2 outside the Red Door. Bi/CNS 150 Lecture 5 Wednesday, October 9, 2013 Revised after lecture 10/9/13 Presynaptic transmitter release. Chapters 9, 12 (co-written by T. Sudhof, one of this week’s Nobel Prize awardees). - PowerPoint PPT Presentation
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Bi/CNS 150 Lecture 5
Wednesday, October 9, 2013 Revised after lecture 10/9/13
Presynaptic transmitter release
Henry Lester’s “office” hours Mon, 1:15-2 PM, Fri 1:15-2 outside the Red Door
Chapters 9, 12 (co-written by T. Sudhof, one of this week’s Nobel Prize awardees)
2
Proof of chemical synaptic transmission, 1921
Vagus nerve runs from the head to the heart
Spontaneous heartbeats in both
hearts are stopped by stimuli to the “upstream”
vagus smoked drum
The diffusible substance:
acetylcholine acting on
muscarinic ACh receptors
[neurotransmitter]
openclosed
chemical transmission atsynapses:
electric field
openclosed
electrical transmission inaxons:
Past lectures:V-gated Na+ channelsV-gated K+ channelsToday: V-gated Ca2+ channels
Next week: Glutamate-gated excitatory (Na+ / K+ / Ca2+) channels
4Figure 9-1
Many basic principles of chemical transmissionanddevelopmental neurosciencewere discovered at the neuromuscular junction (nerve-muscle synapse); acetylcholine is the transmitter.
0.3 µm
Fine structure of the NMJ
Figure 9-1 5
ACh receptors
Incl. acetylcholinesterase
Life cycle of a synaptic vesicle
Figure 12-10 6
Caught by flash-freezing,
invented at Caltech ~ 50 yr ago
A. Van Harreveld
Presynaptic terminal
postsynaptic cell
Like Figure 12-7 7
A. Homogenize brain in isotonic sucrose.
B. Isolate synaptosomes (cut-off nerve terminals)
by differential and sucrose gradient centrifugation
C. Lyse synaptosomes in hypotonic solution to release vesicles.
D. Isolate vesicles by glass bead column chromatography.
Vesicles can be isolated from brain tissue by cell biological methods
Proteins associated with synaptic vesicles, slide 1
8
SynaptophysinSynaptotagmin (the Ca2+ sensor)Snares (residents of either the vesicle [v-snare]
or the target membrane [t-snare])VAMP (also called synaptobrevin), a v-snareSyntaxin, a t-snare that also associates with Ca2+ channels SNAP-25, a t-snare (~25 kD)
ATP-driven proton pump creates concentration gradient that drives neurotransmitter uptake against concentration gradient
(one of three transporters that function in transmitter release)
Proteins associated with synaptic vesicles, slide 2
Atomic-scale structure of (bacterial) Na+ channels (2011, 2012)
As of fall 2013, there are no crystal structures of voltage-gated Ca2+ channels.
From the similarities in sequence, we expect the secondary and tertiary structures to resemble those of K+ and Na+ channels.
A voltage-gated Na+ channel can be changed to a voltage-gated Ca2+ channel by mutating . . .just 2 out of 1800 amino acids
See Table 12-1
13
docked vesicle
voltage-gated Ca2+ channel
neurotransmitter
Electricity, then chemistry triggers synaptic vesicle fusion
See 1st part of Chapter 12
We’ll show a more complete animation in a few minutes
nerve impulseNa+ and K+ channels
14
voltage-gated Ca2+ channel
Electricity, then chemistry triggers synaptic vesicle fusion
Ca2+
docked vesicle
neurotransmitter
See 1st part of Chapter 12
We’ll show a more complete animation in a few minutes
nerve impulseNa+ and K+ channels
15
fused vesicle
Ca2+
neurotransmitter
Electricity, then chemistry triggers synaptic vesicle fusion
See 1st part of Chapter 12
We’ll show a more complete animation in a few minutes
1. The Na+ channels have produced the voltage change (depolarization);
the K+ channels have rendered it brief (~ 1 ms)
2. The Ca2+ channels produce some depolarization, but their main function: to introduce the intracellular messenger Ca2+
Synaptotagmin has as many as 40 Ca2+-binding sites. Perhaps binding of more Ca2+ increases the rate of fusion and/or pushes the vesicle toward the “slow track” and full fusion.