NESC 2570 Study Guide - Final Guide: Patch Clamp, Potassium Channel Blocker, End-Plate Potential
27 Jun 2018
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Describe how small molecule neurotransmitters and neuropeptides are
synthesized and packaged into synaptic vesicles. What happens to these
neurotransmitters once they are released?
Small molecule neurotransmitters are either synthesized locally at the
synapse or they are re taken up by the pre synaptic terminal and are then
packaged into vesicles using a proton gradient that transport the
neurotransmitter into vesicles in the lumen. once that has happened and the
neurotransmitter is released into the synaptic cleft, the neurotransmitter is
utilized again for another round.
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They are different from neuropeptides because neuropeptides are
synthesised into the ER lumen and are then transported into the Golgi.
They are processed so that we get the neuropeptides from the precursors
and then transported. Once, neuropeptides are released, they are released
they are NOT reutilized again
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1)
What experimental approach can be utilized to demonstrate that action
potential-evoked neurotransmitter release requires calcium influx through
voltage gated calcium channels.
Calcium is important for release and that calcium flows in through voltage
gated calcium channels. We can use calcium chelators (compounds that
bind calcium), we can inject them into the presynaptic terminal. This
makes it increasingly more difficult almost impossible to elicit a calcium
release. However, when calcium is injected into the post synaptic terminal,
the post synaptic response is very similar to normal post synaptic
transmission.
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Co variance of post synaptic potential/current
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You can block them using cations or other specific drugs - blocking
calcium influx through voltage gated calcium channels
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2)
Why does 4-aminopyridine, a potassium channel blocker, increase the
amount of neurotransmitter released at the neuromuscular junction?
If you block voltage gated potassium channels, the repolarization during
the action potential is much slower which causes much more calcium
influx, this calcium influx in turn means more neurotransmitter release
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3)
How many acetylcholine molecules elicit a "miniature endplate potential"?
About 1000 - miniature endplate potentials are small excitatory post
synaptic potentials at the endplate (specialize synapse at the neuromuscular
junction) they are spontaneous excitatory post synaptic potentials . So they
do this without an action potential and correspond with the release of one
synaptic vesicle filled with neurotransmitter
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How much neurotransmitter is in one synaptic vesicle?
.04 microvolts in each vesicle - we need about 1000 open
acetylcholine receptors to get one miniature endplate potential.
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4)
The figure shows patch clamp recordings from a neuron in the central
nervous system. In contrast to mEPPs at the neuromuscular junction,
mEPSCs recorded in CNS neurons are very variable in size, ranging from as
little as 5pA to several tens of pA. How can this observation be explained?
Neuromuscular junction has one large compound synapse where many
synaptic vesicles are all lined up and you can record adjacent to the
synapse. This is in contrast to the central nervous system, usually you
record form the soma of the cell. The potential as it propagates to the some
will decay electronically which means that if a potential change is large
(5mV), at the soma it would be much smaller. Synapses are distributed
throughout the dendrites as well, the ones that are close to the soma are
much larger post synaptic potential because the current doesn't have to
travel as far. This is why there is a large size distribution in neurons of
spontaneous post synaptic potentials in the CNS neurons. The largest of
these currents correspond to the synapses that are closest to the soma. In
neurons of the CNS it is hard to figure out neurotransmitter release is in
quanta or not (in packages). No clear cut evidence that ALL
neurotransmitter release is quantal. Some release in the CNS might be kiss
and run, this would imply that this kind of release is not quantal.
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5)
Review Questions
October 25, 2015
9:32 PM
Document Summary
Describe how small molecule neurotransmitters and neuropeptides are synthesized and packaged into synaptic vesicles. They are different from neuropeptides because neuropeptides are synthesised into the er lumen and are then transported into the golgi. They are processed so that we get the neuropeptides from the precursors and then transported. Once, neuropeptides are released, they are released they are not reutilized again. What experimental approach can be utilized to demonstrate that action potential-evoked neurotransmitter release requires calcium influx through voltage gated calcium channels. Calcium is important for release and that calcium flows in through voltage gated calcium channels. We can use calcium chelators (compounds that bind calcium), we can inject them into the presynaptic terminal. This makes it increasingly more difficult almost impossible to elicit a calcium release. However, when calcium is injected into the post synaptic terminal, the post synaptic response is very similar to normal post synaptic transmission.
