post 2

17)This information applies to Questions 17-20:

You are studying a neuron that has a neurotransmitter receptor that has never been studied before. You decide to name this receptor “receptor C” (abbreviated RC), and you do a series of experiments to learn more about it. The receptor is activated by ACh and is metabotropic.

This neuron contains only one type of ion channel, which passes ion W, an anion. This ion channel (a W channel) is voltage-gated, and the probability of opening increases as a function of voltage. Thus, in your experiments you can test the current through these channels by holding the membrane potential at -80 mV, stepping it to +20 mV, and measuring the size of the W current during the voltage step.

You do some experiments to determine whether this is a metabotropic receptor or not, and you determine that it is, in fact, metabotropic.

Question 17: Which of the following experiments would support this finding and why?

	a.
You put GDP-β-S into the neuron and stepped the membrane potential to +20 mV, both with and without ACh present. This decreased the amount of W current. This means that dimerization of the G-protein subunits is required in order for activation of RC to affect the W current.

 	b.
You put GDP-β-S into the neuron and stepped the membrane potential to +20 mV, both with and without ACh present. There was no change in the amount of W current. This means that dimerization of the G-protein subunits is required in order for activation of RC to affect the W current.

 	c.
You put GTP-γ-S into the neuron and stepped the membrane potential to +20 mV, both with and without ACh present. This decreased the amount of W current. This means that dimerization of the G-protein subunits is required in order for activation of RC to affect the W current.

 	d.
You put GTP-γ-S into the neuron and stepped the membrane potential to +20 mV, both with and without ACh present. There was no change in the amount of W current. This means that dimerization of the G-protein subunits is required in order for activation of RC to affect the W current.





18) This question is a continuation of the introductory information given in Question 17.

Now that you know this is a metabotropic receptor, you want to identify the G-protein-coupled signaling pathway it uses to affect W channels (assume it uses one of the main four discussed in the course materials).You are assaying this by applying a depolarizing voltage step, as described above and measuring the W current. Assume only one pathway is used in this cell and the only thing that activates it is RC. That is, only one description below could possibly be accurate and lead to the stated conclusion.


Question 18: Which of the following experiments definitively showed you which pathway it uses?

	a.
You put a drug into the neuron that activates PKC. You then test the W currents and show that there is the same amount of W current with and without ACh present. Therefore, you know RC affects W channels via the cAMP pathway.

 	b.
You put a drug into the neuron that activates PKC. You then test the W currents and show that there is the same amount of W current with and without ACh present.  Therefore, you know RC affects W channels via the phosphoinositol pathway.

 	c.
You put a drug into the neuron that blocks PKC. You then test the W currents and show that there is the same amount of W current with and without ACh present. Therefore, you know RC affects W channels via the cAMP pathway.

 	d.
You put a drug into the neuron that blocks PKC. You then test the W currents and show that there is the same amount of W current with and without ACh present. Therefore, you know RC affects W channels via the phosphoinositol pathway.



19) (IMAGE Y) Next, you want to determine what effect activation of RC by ACh has on the W channels. You do this by stepping the membrane potential as described above, and you get the results in IMAGE Y. The equilibrium potential for W is -75 mV.

Question 19: Which of the following can you accurately conclude based on these data?



	a.
Activating RC decreases the probability of W channel opening

 	b.
Activating RC increases the probability of W channel opening


20)You are studying a glutamatergic synapse you’ve never studied before, and lo and behold, the postsynaptic neuron has C receptors. This is extremely handy, because you already know a lot about RCs, and this means you will be able to complete your PhD thesis and later save the world, based on your data, so hey, everyone wins. However, before all of that, you need to determine how activation of RCs affects the postsynaptic response to glutamate.

In addition to RCs, the postsynaptic cell contains AMPA receptors, but it has no other neurotransmitter receptors. In your experiment, you record the postsynaptic response to the glutamate that is released when you stimulate the presynaptic neuron. You do this both in the absence of ACh and in the presence of ACh. You get one of the three sets of results (a, b, c) shown in IMAGE Z. Based on what you know about RCs and AMPARs, indicate which graph is correct (a, b, or c).