MOD 5 -Soley Valencia

Module 5
SoléyValencia
CBNS 130L
Electrophysiology

Abstract
I made a 2 Cell model and observed the
communication between them while varying
conductance to A,T,AHP, L, C, and M currents and
manipulating GABAa, GABAb, NMDA,AMPA to
ﬁne tune each action potential.

Introduction
Much of the currents that I varied rely on calcium dependent potassium
channels such as C,AHP, and T currents. Calcium dependent potassium channels
have been further studied and have been linked with rhythmic motor
movements sequenced into timing of muscle contractions that rely on
communications between neurons. Scientists found that calcium dependent
potassium channels may be linked to rhythmic movement while studying
Drosophila. BK channels activate with an increase in extracellular calcium and
are involved in fast repolarization and burst ﬁring. Mutations in slo genes that
require BK channels were identiﬁed in movement disorders.The slo gene was
cloned in the Drosophila and it was observed that slo genes encode for calcium
dependent potassium channels and found that they delay repolarization at
neuromuscular junctions (McKiernan 2013).

Methods and Materials
Through “My first Neuron” created my own experiment between 2 Cells by inserting
and removing mechanisms to create the intended parameters.
- Applied A-current first to the excitatory cell then to the inhibitory cell changed Cell 1 AMPA = 0.1 NMDA
= 0.001 Amplitude = 2n and Cell 2 GABAa = 0.01 GABAb = 0.001 gkbar_iA = 0 then compared these
results to one I had set with gkbar_iA = 0.000345.Then applied changes to the second cell; Cell 1 AMPA =
0.1 NMDA = 0.001 Amplitude = 3nA Cell 2 GABAa = 0.01 GABAb = 0.001 gkbar_iA = 0.001.
- Applied T-Current first to the excitatory cell then the inhibitory Cell 1 was set to GABAa = 0.4 GABAb =
0.1Cell 2: AMPA = 0.1 NMDA = 0.01 iT = 0.005 then these results were compared with a graph setting
Cell 1: GABAa = 0.4 GABAb = 0.1 Cell 2: AMPA = 0.1 NMDA = 0.01 gkbar_iT = 0.007 Base Current =
5nA and applied Initial voltage of -80mV with 1000ms.
- AHP current is applied while its conductance is varied when setting AHP first to the excitatory neuron
then to the inhibitory neuron. Settings were set to Cell 1: GABAa = 0.4 GABAb = 0.1Cell 2: AMPA = 0.1
NMDA = 0.01 gkbar_iAHP = 0.01 iT= 0.008 and a Base Current = 2nA [Ca++]out = 0.1mM while maintaing
an initial voltage of -80mV. I then compared these results with settings Cell 1: GABAa = 0.2 GABAb = 0.1
gkbar_iAHP = 0.002 [Ca++]out = 0.1mM Cell 2: AMPA = 0.1 NMDA = 0.01 gkbar_iT = 0.008 Base
Current = 2nA.
- L and C current is applied while its conductance is varied by first applying it to an excitatory and then to
the inhibitory neuron.The settings Cell 1: GABAa = 0.3 GABAb = 0.1 Cell 2: AMPA = 3 NMDA = 0.01 iL
= 0.000276 iC = 0.00345 Base Current = 3nA and compared the results with a graph set to Cell 1: GABAa =
0.3 GABAb = 0.1 Base Current = 1nA iL= 0.003 iC= 0.004 Cell 2: AMPA = 3 NMDA = 0.01
Base Current = 3nA.
- M Current is applied first on the excitatory neuron then on the inhibitory neuron while the conductance is
varied. I set Cell 1: GABAa = 1 GABAb = 0.1 Base Current = 1nA Cell 2: AMPA = 0.3 NMDA = 3 Base
Current = 5nA iM = 0.001 while maintaining the initial voltage at -65mV. I compared these results with
settings I set the graph in at Cell 1: GABAa = 1 GABAb = 0.1 Base Current = 1nA iM = 0.0009 Cell 2:
AMPA = 0.1 NMDA = 3 Base Current = 3nA

Cell 1 (Excitatory) Cell 2 (Inhibitory)
The graph on the left shows Cell 2 ﬁring more frequently since the conductance of A-Current is set
to 0. Cell 1 depolarizes Cell 2 which sends an IPSP back to Cell 1, this is why the amplitude of Cell 2
is smaller.The graph on the right, Increase GABAa to 0.1 to 2 didn’t inhibit Cell 2 even when it was
successfully responding with IPSP to Cell 1 with a GABAa level of 0.01.This is because I introduced
A-current at 0.00345 settings which inhibited Cell 2 from ﬁring.To overcome iA inhibition on Cell 2
I increased Cell 1 Base current to 3nA.
Cell 1: AMPA = 0.1 NMDA = 0.001 Amplitude = 2nA
Cell 2: GABAa = 0.01 GABAb = 0.001 gkbar_iA = 0
A-Current Applied to Cell 2
Cell 2: GABAa = 2 GABAb = 0.001 gkbar_iA = 0.000345

The graph on the left; Cell 2 shows less inhibition on Cell 1 because I changed GABAa to 0.01
keeping everything else the same.The graph on the right; I lowered A-current conductance on Cell 2
which allowed it to send an IPSP to Cell 2. Cell 1 is able to still send an EPSP to Cell 2 after it
receives an IPSP because I added a base current injection of 3nA.
Cell 2: GABAa = 0.01 GABAb = 0.001 gkbar_iA = 0.00345
Cell 2: GABAa = 0.01 GABAb = 0.001 gkbar_iA = 0.001

The graph on the left; with an increased gkbar_iA conductance from 0.00345 to 0.06 Cell 1 became
too inhibited to reach threshold and have an action potential so that it could no send an IPSP to Cell
2, therefore, we see no Action potential from Cell 2.The graph on the right;A-current conductance
is set to 0.01 and Cell 2 is sending an IPSP to Cell 1 so that Cell1 action potentials are smaller in
amplitude in spite of Cell 1 sending less EPSP to Cell 2 because of the increase IPSP sent on Cell1.
Cell 1: AMPA = 0.1 NMDA = 0.001
Amplitude = 3nA gkbar_iA= 0.06
Cell 2: GABAa = 0.1 GABAb = 0.001
Cell 1: AMPA = 0.1 NMDA = 0.001
Amplitude = 3nA gkbar_iA= 0.01

Cell 1 (Inhibitory) Cell 2 (Excitatory)
InitialVoltage -80mV
The graph on the left; Cell 2 is activating faster than there are sodium channels available because
sodium channels have not recovered by the time Cell 2 has recovered so that its action potential
amplitude decrease sending less EPSP to Cell 2.The graph on the right;T-current on Cell 1 activates
due to the initial voltage set at -80mV so that there is an increase influx of calcium. I also increased
potassium outside the Cell 1 to 5mM leading to a further depolarization as potassium influxes. Cell 2
sent an EPSP that depolarized Cell 1 too much. It cause it to increase firing rate faster than sodium
channels available because sodium channels have nor recovered at that time so that there isn’t
enough sodium for the next action potential.The decrease in action potentials stopped Cell 1 from
firing an EPSP to Cell 2 so that it was able to depolarize, but because I also added -20nA as base
current, it cause T-current to activate and influx of calcium further drove the cell to fire more action
potentials
Cell 2: AMPA = 0.1 NMDA = 0.01
iT = 0.005
[k+]o = 5mM
Cell 2: AMPA = 0.1 NMDA = 0.01
iT = 0.005 Amplitude -20nA
T-Current Applied on 2 Cell Model

Cell 1 (inhibitory) Cell 2 (Excitatory)
iT inﬂux calcium into Cell 2, causing action potential at Cell 2 so that
Cell 2 ﬁres EPSP to Cell 1. In turn, Cell , sends an IPSP to Cell 2 hyperpolarizing Cell 1,
plus calcium gated potassium dependent and channels are activated causing further
hyperpolarization of cell 2.
Cell 2: AMPA = 0.1 NMDA = 0.01 gkbar_iT = 0.007
1000 ms

By adding 5nA of base current to the excitatory cell, it cause it to ﬁre an stronger EPSP
to Cell 1 which sent an a strong IPSP back to Cell 2 but, since 5nA of current was
applied to Cell 2, it prevented it from staying in a state of hyperpolarization so that it
was able to ﬁre subsequent EPSP to Cell 1.
Cell 2: AMPA = 0.1 NMDA = 0.01 gkbar_iT = 0.007 Base Current = 5nA
1000 ms

In spite of adding more iAHP to Cell 2, managed to depolarize due to the addition of
2nA o base current. Because initial voltage was set to -80mV, iT current was able to
activate that allowed an inﬂux of calcium which led to the opening of potassium
channels that hyperpolarized the cell. iT and iAHP are both calcium dependent
potassium channels so both were working on inhibiting the cell right after reaching a
depolarized state of 59mV.
AHP-Current Applied to Cell 2
Cell 2: AMPA = 0.1 NMDA = 0.01 gkbar_iAHP = 0.01 gkbar_iT= 0.008
Base Current = 2nA [Ca++]out = 0.1mM
1000 ms

I added 2nA of current to Cell 2 but little IPSP from Cell 1 was received from Cell 2,
which lowered Cell 2 because of the base current and because Cell1 has 0.1 mM of
extracellular calcium so that there will be less calcium available inside the cell.
AHP-Current Applied to Cell 1
Cell 1: GABAa = 0.2 GABAb = 0.1 gkbar_iAHP = 0.002 [Ca++]out = 0.1mM
Cell 2: AMPA = 0.1 NMDA = 0.01 gkbar_iT = 0.008 Base Current = 2nA
1000 ms

Cell 2 reaches threshold and displays action potentials because iL increases
calcium inﬂux an iC is calcium dependent potassium channel. I also added 3nA of
base current to Cell 2 so that it does not stay hyperpolarized for long after
receiving an IPSP from cell 2.
L & C-Current Applied to Cell 2
Cell 2: AMPA = 3 NMDA = 0.01 iL = 0.000276 iC = 0.00345
Base Current = 3nA
1000 ms

Cell 1 is very depolarized because there is an influx of calcium due to iL and iC current
which are dependent in the influx of calcium.When calcium binds to potassium
channels it hyperpolarizes the cell so that
Cell 1 stops sending IPSP to Cell 2 and Cell 2 can then fire back an EPSP to Cell 1.
L & C-Current Applied to Cell 1
Cell 1: GABAa = 0.3 GABAb = 0.1 Base Current = 1nA iL= 0.003 iC= 0.004
Cell 2: AMPA = 3 NMDA = 0.01 Base Current = 3nA
1000 ms

I had to add 5nA of current to Cell 2 so that it could ﬁre because otherwise iM
would cause Cell 2 to become inhibited, and would have otherwise stopped it
from producing an EPSP to Cell 1.
M-Current Applied to Cell 2
Cell 1: GABAa = 1 GABAb = 0.1 Base Current = 1nA
Cell 2: AMPA = 0.3 NMDA = 3 Base Current = 5nA iM = 0.001
1000 ms

iM current is inhibiting Cell 2 so that it sends a weaker IPSP to Cell 2. I added base
current to Cell 2 so that it wouldn’t stay hyperpolarized. Otherwise, we wouldn’t be
able to see action potentials from Cell 2, which would make Cell 2 stop sending EPSP
to Cell 1 and communication between the cells would stop.
M-Current Applied to Cell 1
Cell 1: GABAa = 1 GABAb = 0.1 Base Current = 1nA iM = 0.0009
Cell 2: AMPA = 0.1 NMDA = 3 Base Current = 3nA
1000 ms

Discussion
- The more A-Current Conductance that is added to Cell 2 the less excitable it becomes which in
turn, sends less IPSP signals to Cell 1.
- When a neuron is overexcited the amplitude of its action potentials decreases because it is ﬁring
at a faster rate than that of the recovery of sodium channels, meaning that without sodium available
threshold can’t be reached and no action potentials are seen.
- When the excitatory neuron is stimulated so that it produces a strong EPSP the inhibitory neuron
will respond strongly and inhibit the excitatory neuron so that communication between the neurons
becomes interrupted.
- L-Current is a persistent current that lets calcium inside the cell. Once calcium is inside the cell, it
can then help modulate other channels such as, C and AHP currents.AHP is calcium dependent
potassium current.
- When T-Current is equal to zero, we don’t have Ca++ spikes but, we still get depolarization even
though it does not reach threshold so that we observe no bursts. Given that it is active at
hyperpolarized state, the cell that was observed without iT current needed a positive base currents.
- C-Current is calcium dependent potassium channel. Once calcium is inside the cell it tries to reach
calcium equilibrium which pushes the membrane potential close to threshold where sodium
channels act as positive feedback and start ﬁring.At this more depolarized membrane potential
potassium channels are activated leading to the hyperpolarization of the cell.
- M-Current is activated when current shows depolarization for a long time which means that iM
can modulate long term neuronal states.

Literature Cited
"McKiernan (2013) Eﬀects of manipulating slowpoke calcium-dependent potassium channel expression on
rhythmic locomotor activity in Drosophila larvae. PeerJ 1:e57." National Center for Biotechnology
Information. U.S. National Library of Medicine, n.d. Web. 01 Sept. 2013.

MOD 5 -Soley Valencia

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