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Lab Practicum Review – Questions & Solutions
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Lab Practicum Review – Questions & SolutionsWhat is the effect of the TRPV1 channel opening?
a. Negative ions flow outward
b. Positive ions flow outwards
c. Positive ions flow inwards
d. Negative ions flow inward ✔️Ans - Positive ions flow inward
**Positive ions (most importantly calcium) enter the cell by flowing down
their concentration gradient. This causes a graded depolarisation.
What is an important characteristic of the buffer used for studying sodium in
patch clamp experiments?
a. One that blocks sodium channels
b. One that blocks sodium and potassium channels
c. One that blocks potassium and calcium channels
d. One that blocks chloride channels ✔️Ans - One that blocks potassium and
calcium channels
**We want to block potassium and calcium channels so that we are only
observing the current flowing through sodium channels. This effectively
means we will be observing only the influx of sodium into the neuron
If this cell is a neuron, using the voltage clamp to change the cell membrane
potential from -70.0 mV to -5.0 mV should cause:
a. A current that indicates that sodium continues to enter the cell as long as
the membrane potential is set to -5 mV
b. A current that indicates a large amount of sodium briefly entering the cell
c. No change in sodium current cross the cell
d. A current that indicates a large amount of sodium briefly leaving the cell
✔️Ans - A current that indicates a large amount of sodium briefly entering
the cell
**Depolarization of a neuron beyond the threshold should cause the voltage-
gated sodium channels to briefly open, with an influx of sodium and then
close.
(Based on graph) Capsaicin...
,a. Opens potassium channels resulting in a current spike inwards
b. Blocks the voltage-gated sodium channels
c. Triggers the voltage-gated sodium current
d. Opens the TRPV! channels with no effect on sodium channels ✔️Ans -
Opens the TRPV1 channels with no effect on sodium channels
**Action potential still occurs when the membrane potential is shifted from -
70 mV to -5 mV, capsaicin likely does not affect the voltage-gated sodium
channels
** it could open for TRPV1 channels, no direct evidence, but best option
**No action potential at -70 mV
** If capsaicin opened potassium channels, current would go int he opposite
direction
What action does the drug Lidocaine produce?
a. Activates the TRPV1 channel
b. Opens potassium channels from outside the cell
c. Triggers action potential
d. Inhibits voltage-gated sodium channels ✔️Ans - Lidocaine inhibits the
voltage-gated sodium channels
** Due to buffer choice, the current only represents the inward flow of sodium
ions through the voltage-gated sodium channels
** Relatively flat line of the current in the bottom graph around 0 = lidocaine
inhibits voltage-gated sodium channels from opening
What action does the drug Rebine produce?
a. Opens potassium channels
b. Inhibits voltage-gated sodium channels
c. Triggers action potential
d. No impact on the cell ✔️Ans - Rebine seems to have no impact on the cell
**Action potential still occurs when membrane potential goes from -70 mV to
-5 mV. Rebine seems to not affect the voltage-gated sodium channels.
All the experiments so far are consistent with:
a. Rebine and capsaicin both bind to the TRPV1 channel
b. Rebine inhibits capsaicin's ability to bind to the TRPV1 channel
, c. Rebine requires open TRPV1 channels in order to inhibit voltage-gated
channels
d. Rebine opens the voltage-gated sodium channels by binding to those
channels from the outside of the cell. ✔️Ans - Rebine requires open TRPV1
channels in order to inhibit voltage-gated channels
**If Rebine opened sodium channels from the outside = induce action
potential on its own
**Binding of refine and capsaicin together to the TRPV1 channel would not
inhibit the action potential, nor would blocking the capsaicin binding tot the
TRVP1 channel
What would be the effect on the membrane voltage of tripling the clamped
current while applying Rebine and capsaicin together to the nociceptor?
a. Membrane voltage will increase without an action potential occurring
b. Membrane voltage will remain constant
c. The neuron would depolarize
d. Membrane voltage would decrease and an action potential will be observed
✔️Ans - Membrane voltage will increase without an action potential
occurring
**Even increasing the current to 3 times higher while applying capsaicin and
Rebine to nociceptor does not trigger an action potential.
**Increasing current flow so more positive ions enter the nociceptor does
raise the membrane voltage, even to above the neurones activation threshold.
However, an action potential requires the opening of the voltage-gated
sodium channels which are inhibited
What does a longer latency to withdrawal time reflect?
a. Faster reflex due to a higher temperature
b. Slower reflex due to being less sensitive to pain
c. Slower reflex due to being more sensitive to pain
d. Faster reflex due to being more sensitive to pain ✔️Ans - Slower reflex
due to being less sensitive to pain
**Lidocaine inhibit the activation of nociceptors
What is the significance of Rebine entering the cell through the TRPV1
channel?
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