Indirect Mechanisms Of Synaptic Transmission

1. What are the two mechanisms by which G-proteins affect cell activity?

1. Through G-protein coupled receptors; when the G-protein is activated by it's receptor the alpha and beta/gamma subunits dissociate. The free subunits modulate the activity of the intracellular targets. When Ach binds to its muscarinic receptor on cells in the atrium of the heart, a G-protein is activated. The free beta/gamma subunit binds to ion channels, thereby slowing heart rate.

2. Activation of enzymes can also produce intracellular second messengers. Activation of G-Protein in cardiac muscle cells--> binding of NE to beta-adrenergic receptors --->alpha and beta/gamma subunits--->stimulate the enzyme adenylyl cyclase--> increased cAMP---> cAMP-dependent protein kinase---> phosphorylation. (may result in long lasting effects, and cascade of events)

Activation of G-Protein in liver cells leads to the release of digestive enzymes.

Activation of G-Protein in cardiac muscle cells leads to the activation of apoptosis.

Activation of G-Protein in nerve cells leads to direct muscle contraction and relaxation.

G-Proteins primarily function through G-protein coupled receptors and enzyme activation. These mechanisms play important roles in modulating cell activity through various pathways as described in the correct answer.

Explanation

G-Proteins primarily function through G-protein coupled receptors and enzyme activation. These mechanisms play important roles in modulating cell activity through various pathways as described in the correct answer.

2. What are direct targets for transmitter activation?

GABA receptors

Potassium and Calcium channels.

Sodium channels

Chloride channels

Potassium and Calcium channels are directly targeted for activation by transmitters, while Sodium channels, Chloride channels, and GABA receptors are not typically activated in the same manner.

Explanation

Potassium and Calcium channels are directly targeted for activation by transmitters, while Sodium channels, Chloride channels, and GABA receptors are not typically activated in the same manner.

3. What effect does opening of potassium (via indirectly acting transmitters) channels have on N-type calcium channels?

The inhibit the calcium channels in the sympathetic neurons and increase the probability that calcium channels open in response to depolarization in cardiac muscle cells.

B. They decrease the probability of calcium channels opening in both sympathetic neurons and cardiac muscle cells.

A. They have no effect on N-type calcium channels.

C. They only affect calcium channels in cardiac muscle cells but not in sympathetic neurons.

Opening of potassium channels indirectly affects N-type calcium channels by inhibiting them in the sympathetic neurons and by increasing the probability of calcium channels opening in response to depolarization in cardiac muscle cells.

Explanation

Opening of potassium channels indirectly affects N-type calcium channels by inhibiting them in the sympathetic neurons and by increasing the probability of calcium channels opening in response to depolarization in cardiac muscle cells.

4. Draw a picture of the metabotropic or G-protein coupled receptor and explain it.

See diagram

Discuss the functions of G-protein coupled receptors without mentioning their activation mechanisms.

Explain the signaling pathway of metabotropic receptors without detailing their structure.

Describe the structure of the G-protein coupled receptor without any visual aid.

The question requires the individual to visually represent and explain the structure of a metabotropic or G-protein coupled receptor. The correct answer directs the examinee to a diagram to better understand the concept visually. The incorrect answers either focus on describing the structure without visualization, discussing signaling pathways without emphasizing structure, or explaining functions without activation mechanisms.

Explanation

The question requires the individual to visually represent and explain the structure of a metabotropic or G-protein coupled receptor. The correct answer directs the examinee to a diagram to better understand the concept visually. The incorrect answers either focus on describing the structure without visualization, discussing signaling pathways without emphasizing structure, or explaining functions without activation mechanisms.

5. What are the four different types of G-protein structures?

Gr--> Regulates adenylyl cyclase activity

Gs--->Stimulate adenylyl cyclase
Gi---> Inhibit adenylyl cyclase
Gq--> couples to phospholipase
G12---> unknown targets

Go--> Inhibits phospholipase activation

Ga--> Activates adenylyl cyclase

The correct answer includes Gs, Gi, Gq, and G12 as the four different types of G-protein structures, each with their specific functions in cellular signaling pathways.

Explanation

The correct answer includes Gs, Gi, Gq, and G12 as the four different types of G-protein structures, each with their specific functions in cellular signaling pathways.

6. Draw a diagram and describe how indirectly coupled transmitter receptors act through G proteins.

G proteins dissociate into alpha/beta and beta/gamma subunits upon binding of a neurotransmitter receptor.

The receptors directly bind to G proteins and activate them without any dissociation process.

GTP on the alpha subunit is exchanged for GDP causing the activation of the G protein.

Activation of a metabotropic receptor by its agonist on the extracellular side, activates a G-protein. The alpha subunit along with GDP dissociate from beta/gamma subunits. The GDP on the alpha subunit is exchanged for GTP (GDP is replaced with GTP), this causes the dissociation of the subunits. The free proteins bind and modulate the activity of their target proteins.

The correct process involves GDP being replaced with GTP on the alpha subunit of the G protein, leading to dissociation of the subunits and subsequent modulation of target protein activity.

Explanation

The correct process involves GDP being replaced with GTP on the alpha subunit of the G protein, leading to dissociation of the subunits and subsequent modulation of target protein activity.

7. What effect does the free alpha subunit have?

It has GTpase activating proteins or GAPs, which influences the rate at which GTP bound to the alpha subunit is hydrolyzed.

It enhances the binding of GDP to the alpha subunit.

It inhibits the release of GDP from the alpha subunit.

It acts as a kinase and phosphorylates other subunits of the G protein.

The correct answer explains the role of GTpase activating proteins (GAPs) in influencing the hydrolysis of GTP bound to the alpha subunit. The incorrect answers provide misleading information regarding the effects of the free alpha subunit.

Explanation

The correct answer explains the role of GTpase activating proteins (GAPs) in influencing the hydrolysis of GTP bound to the alpha subunit. The incorrect answers provide misleading information regarding the effects of the free alpha subunit.

8. What are the two mechanisms that mediate desensitization?

1. Enzymatic degradation of G-proteins.

3. Inhibition of signaling pathways by G-proteins.

1. A Second messanger regulated kinase, such as cAMP-indepentant protein kinase, phosphorylates G-protein-coupled receptors blocking their interaction with G-proteins( this type of mechanism may be non selective: more than one transmitter may activate cAMP-dependent protein kinase, it may phosphorylate more than one type of G-protein coupled receptor).
2. There is also selective phosphorylaytion of activated receptors by a specific G-protein coupled receptor kinase or GRK, such as beta -adrenergic recrptor kinase (BARK). Then a protein of the arrestin family binds to the phosphroylated receptor, blocking its ability to activate G-proteins and thereby terminating the response.

2. Direct activation of G-proteins by G-protein coupled receptors.

Desensitization of receptors involves phosphorylation of activated receptors by kinases or specific GRKs, leading to the blocking of G-protein interactions and termination of the response. Enzymatic degradation of G-proteins, direct activation of G-proteins by receptors, and inhibition of signaling pathways by G-proteins are not mechanisms involved in desensitization.

Explanation

Desensitization of receptors involves phosphorylation of activated receptors by kinases or specific GRKs, leading to the blocking of G-protein interactions and termination of the response. Enzymatic degradation of G-proteins, direct activation of G-proteins by receptors, and inhibition of signaling pathways by G-proteins are not mechanisms involved in desensitization.

9. What effect does Ach binding have on mAch-R in the heart?

It inhibits the activity of potassium channels, leading to cell depolarization.

It causes the closing of sodium channels, leading to depolarization.

It causes the opening of potassium channels, thus causing the cell to hyperpolarize.

It stimulates the release of calcium ions, causing the cell to contract.

When Ach binds to mAch-R in the heart, it typically leads to the opening of potassium channels, which causes hyperpolarization of the cell. This hyperpolarization has a distinct effect on the cell's electrical activity.

Explanation

When Ach binds to mAch-R in the heart, it typically leads to the opening of potassium channels, which causes hyperpolarization of the cell. This hyperpolarization has a distinct effect on the cell's electrical activity.

10. How has experimentation shown the effect of muscarinic receptors and potassium channels when activated?

Activation of muscarinic receptors is coupled to opening of potassium channels by G-proteins. It was found the intracellular GTP is required, the activation of potassium channels by muscarinic agonists is greatly prolonged by intracellular application of a nonhydrolyzable analgue of GTP (GPP) and that muscarinic activation of potassium channels is blocked by pertusis toxin which activated Gi proteins.

Activation of muscarinic receptors is coupled to closing of potassium channels by G-proteins.

Intracellular application of GTP inhibits the activation of potassium channels by muscarinic agonists.

Muscarinic activation of potassium channels is enhanced by pertussis toxin instead of being blocked.

Experimental evidence has shown that activation of muscarinic receptors is indeed coupled to opening of potassium channels by G-proteins. The correct answer highlights the key findings from these experiments.

Explanation

Experimental evidence has shown that activation of muscarinic receptors is indeed coupled to opening of potassium channels by G-proteins. The correct answer highlights the key findings from these experiments.

11. What were the findings of the experiment regarding the inside out membrane patches?

C. Applying the subunit externally caused sodium channels to open instead of potassium channels.

It was shown that when pure recombinant beta/gamma subunit was applied to the intracellular side of the membrane through the patch potassium channels opened.

B. The potassium channels on the extracellular side of the membrane closed when the subunit was applied internally.

A. The membrane patches became less stable when exposed to pure recombinant beta/gamma subunit.

The correct answer describes the direct effect of applying the subunit internally on the potassium channels, resulting in their opening.

Explanation

The correct answer describes the direct effect of applying the subunit internally on the potassium channels, resulting in their opening.

12. What was responsible for the opening of potassium channels?

It demonstrated that the beta/gamma was responsible for the opening of potassium channels, not the alpha subunit.

The delta epsilon subunit

The zeta subunit

The alpha subunit

13. What was the effect observed when muscarinic agonists were added to the patch clamp solution?

Calcium cell activity was increased when muscarinic agonists were added to the patch clamp solution.

Chloride cell activity was drastically decreased when muscarinic agonists were added to the patch clamp solution.

Potassium cell activity was increased. But when muscarinic solution was added to the bath solution then there was no effect on potassium channels.

Sodium cell activity was inhibited when muscarinic agonists were added to the patch clamp solution.

The correct answer explains the specific effect observed on potassium cell activity in the patch clamp solution and highlights the lack of effect on potassium channels when the muscarinic solution was added to the bath solution.

Explanation

The correct answer explains the specific effect observed on potassium cell activity in the patch clamp solution and highlights the lack of effect on potassium channels when the muscarinic solution was added to the bath solution.

14. What does it mean when a cell is membrane delimited?

It meant that direct, mechanism of G protein action reflects the limited range over which beta/gamma subunits can act. (the activation only occured intracellualrly)

It means that the cell's membrane completely surrounds the cell nucleus.

It means that the cell membrane is not involved in any cellular processes.

It means that the cell's membrane is impermeable to all substances.

When a cell is membrane delimited, it refers to the limited range over which certain cellular components or processes can act within the cell, specifically in relation to G protein action.

Explanation

When a cell is membrane delimited, it refers to the limited range over which certain cellular components or processes can act within the cell, specifically in relation to G protein action.

15. Describe how binding of ACh effects the activity on the extracellular side of the cell.

Once ACh binds to the receptor it activates the heterometric G-protein on the intracellular side of the membrane. The GDP is swapped for the GTP and the subunits dissociate. The alpha subunit then activates target proteins, as does the beta/gamma complex (which activates the potassium channel). Then on the alpha subunit GTP is swapped for GDP allowing all three of the subunits to assocate, this occurs because of Pi and inorganic phosphate. Then the process can occur again as long as the lignd is activating the receptor.

ACh binding results in the release of neurotransmitters into the synapse.

ACh binding leads to the depolarization of the cell membrane.

ACh binding causes the cell membrane to become impermeable to ions.

When ACh binds to its receptor, it activates the G-protein on the intracellular side, leading to a series of reactions that ultimately affect the cell's activity. The incorrect answers do not accurately depict the sequence of events following ACh binding.

Explanation

When ACh binds to its receptor, it activates the G-protein on the intracellular side, leading to a series of reactions that ultimately affect the cell's activity. The incorrect answers do not accurately depict the sequence of events following ACh binding.

16. What effect does adding beta/gamma subunit to the intracellular side of the patch have?

Activation of potassium channels

Similar results as seen when ACh is added to the extracellular side of the patch.

Decreased receptor expression

Increased calcium influx

Adding beta/gamma subunit to the intracellular side of the patch results in similar outcomes as if ACh was added to the extracellular side, leading to specific cellular responses.

Explanation

Adding beta/gamma subunit to the intracellular side of the patch results in similar outcomes as if ACh was added to the extracellular side, leading to specific cellular responses.

17. What was observed in the experiment on sympathetic ganglion frog cells?

It was observed that NE release has no effect on any type of receptors in sympathetic ganglion frog cells.

It was found that Ne release not only acts on postsynptic target cells but on presynaptic terminals themselves. More specifically NE interacts with alpha2- adrenergic receptors, these are referred to autoreceptors. When activated they reduce the probablility of opening N-type calcium channels.

The experiment showed that NE release only affects postsynaptic target cells in sympathetic ganglion frog cells.

The experiment concluded that NE release enhances the opening probability of N-type calcium channels in sympathetic ganglion frog cells.

The correct answer explains the specific interaction of NE with alpha2-adrenergic receptors and how it affects the opening probability of N-type calcium channels in sympathetic ganglion frog cells.

Explanation

The correct answer explains the specific interaction of NE with alpha2-adrenergic receptors and how it affects the opening probability of N-type calcium channels in sympathetic ganglion frog cells.

18. What controls the release of NT from sympathetic neurons?

Calcium entering through N-type channels.

ACh binding to muscarinic receptors.

ATP production in mitochondria.

Sodium influx through voltage-gated sodium channels.

The release of neurotransmitters (NT) from sympathetic neurons is primarily controlled by calcium entering through N-type channels, which triggers the exocytosis of synaptic vesicles containing the NT. Other mechanisms such as ATP production in mitochondria, sodium influx through voltage-gated sodium channels, and ACh binding to muscarinic receptors do not directly control the release of NT from sympathetic neurons.

Explanation

The release of neurotransmitters (NT) from sympathetic neurons is primarily controlled by calcium entering through N-type channels, which triggers the exocytosis of synaptic vesicles containing the NT. Other mechanisms such as ATP production in mitochondria, sodium influx through voltage-gated sodium channels, and ACh binding to muscarinic receptors do not directly control the release of NT from sympathetic neurons.

19. How do NE neurotransmitters function presynaptically and what is their function?

NE neurotransmitters inhibit the reuptake of serotonin at the synapse, leading to prolonged signal transmission.

NE neurotransmitters are released post-synaptically and act on beta receptors to increase calcium influx, enhancing transmitter release.

NE neurotransmitters bind to muscarinic receptors, increasing the release of acetylcholine and promoting parasympathetic responses.

Neurons release NE at presynaptic terminals and acts back on itself via alpha2 adrenergic receptors. This reduces the prbability of N-type CA2+ channels opening. The activation of Alpha2 adrenergic receptors activate G-proteins. The activated beta/gamma complex bind CA2+ channels decreasing CA2+ influx and thus limiting furthering transmitter release from sympathetic ganglia.

NE neurotransmitters function presynaptically by acting on alpha2 adrenergic receptors to decrease calcium influx, limiting further neurotransmitter release.

Explanation

NE neurotransmitters function presynaptically by acting on alpha2 adrenergic receptors to decrease calcium influx, limiting further neurotransmitter release.

20. Describe the findings of the experiment presented in figure 10.6B.

The graph shows that NE increases the release of neurotransmitter from sympathetic ganglia.

The transmitter release was evoked by hyperpolarization rather than depolarization with a solution containing 50mM of K+.

Ganglia were loaded with radioactive DA and then enclosed in a perfusion chamber.

This graph shows that NE reduces the release of neurotransmitter from sympathetic ganglia. Ganaglia were loaded with radioactive NE and then enclosed in a perfusion chamber. The tranmitter release was evoked by depolorization with a solution containing 50mM of K+. Addition of 30mM of NE caused a decrease in the opening of K+ channels(reduced the amount of NT released in response to K+ channel depolariztion).

The correct answer describes the experiment accurately, showing how NE reduces neurotransmitter release. The incorrect answers provide alternative scenarios that do not match the findings outlined in the graph.

Explanation

The correct answer describes the experiment accurately, showing how NE reduces neurotransmitter release. The incorrect answers provide alternative scenarios that do not match the findings outlined in the graph.

21. When is inhibition of CA2+ activity in cell attached patches observed?

When G-protein is not present in the cell attached patches.

When NE is added to the extracellular solution.

When NE is added to the recording pipette, but not when added to the extracellular solution. This suggests that there is a direct interaction between G-protein and Ca2+ channels. (NE effects the duration of the N-type CA2+ when they are open. ). Results of this experiment indicte that beta/gamma subunits inhibit N-Type calcium channels

When CA2+ is added to the recording pipette.

The correct answer highlights the specific conditions under which inhibition of CA2+ activity is observed in cell attached patches, emphasizing the role of NE and the direct interaction between G-protein and Ca2+ channels. The three incorrect answers provide plausible but incorrect scenarios that do not result in the observed inhibition.

Explanation

The correct answer highlights the specific conditions under which inhibition of CA2+ activity is observed in cell attached patches, emphasizing the role of NE and the direct interaction between G-protein and Ca2+ channels. The three incorrect answers provide plausible but incorrect scenarios that do not result in the observed inhibition.

22. What is the impact of inhibitory effects on transmitters?

They have no effect on the release of transmitters.

They slow down the regulation of release of transmitters.

They enhance the release of transmitters.

They provide a rapid and localized mechanism for regulation of relsease.

Inhibitory effects on transmitters provide a rapid and localized mechanism for regulation of release by controlling the amount of transmitters released.

Explanation

Inhibitory effects on transmitters provide a rapid and localized mechanism for regulation of release by controlling the amount of transmitters released.

23. How does activation of Beta-adrenergic receptors in cardiac muscle affect calcium channels and what transmitter is used?

Using the cell attactched mode of the patch clamp technique stimuluation of the beta -adrenergic receptor agonist (NE) produce an increase in calcium channel activity.

Activation of Beta-adrenergic receptors in cardiac muscle has no effect on calcium channels and uses acetylcholine as the transmitter.

Activation of Beta-adrenergic receptors in cardiac muscle decreases calcium channel activity using the patch-clamp technique.

Using the whole-cell configuration of the patch clamp technique, activation of Beta-adrenergic receptors in cardiac muscle results in a decrease in calcium channel activity with dopamine as the transmitter.

Activation of Beta-adrenergic receptors in cardiac muscle using the cell-attached mode of the patch clamp technique and stimulating with the beta-adrenergic receptor agonist (NE) results in an increase in calcium channel activity. The incorrect answers provide alternative scenarios that do not align with the known physiological responses.

Explanation

Activation of Beta-adrenergic receptors in cardiac muscle using the cell-attached mode of the patch clamp technique and stimulating with the beta-adrenergic receptor agonist (NE) results in an increase in calcium channel activity. The incorrect answers provide alternative scenarios that do not align with the known physiological responses.

24. Where should the agonist be placed to produce the described effects?

It should be placed on the cell membrane directly.

It can be added in pippette or to the medium bathing bathing the cell causes an increase in calcium channel activity within the patch.

It should be introduced into the nucleus of the cell.

It should be added to the extracellular matrix surrounding the cell.

The correct placement of the agonist is essential for its intended effects on calcium channel activity.

Explanation

The correct placement of the agonist is essential for its intended effects on calcium channel activity.

25. Please describe the following figure.

B) Decrease of sodium current produced by alpha-adrenergic receptors.

A) Increas of calcium current produced by beta-adrenergic receptors. Addition of NE increases AP amplitude and duration and tension produced by cardiac muslce cells.
B) CA2+ current measured under voltage clamp conditions in absence of NE , a beta-adrenergic receptors

Overall it shows NE increases CA2+ current in Heart cells

D) Increase of chloride current due to parasympathetic stimulation.

C) No change in potassium current with the addition of NE.

The correct answer describes the increase of calcium current produced by beta-adrenergic receptors and the overall effect of NE on CA2+ current in heart cells. The incorrect answers provide alternative scenarios that are not supported by the figure or the given information.

Explanation

The correct answer describes the increase of calcium current produced by beta-adrenergic receptors and the overall effect of NE on CA2+ current in heart cells. The incorrect answers provide alternative scenarios that are not supported by the figure or the given information.

26. Draw and explain the diagram for the phosphorylation of CA2+ channels by PKA. (Describe the interaction of beta-adrenergic receptors acting through the intracellular second messenger cAMP).

Activation of beta-adrenergic receptors leads to the inhibition of cAMP production.

Diagram. The diagram explains how Beta-adrenergic receptors act through the intracellular second messenger cAMP to increase calcium channel activity.
The binding of NE to beta-adrenergic receptors activates, through a G-protein, the enzyme adencylyl cyclase. Adenylyl cyclase catalyzes the conversion of ATP to cAMP. As the conversion of cAMP increases, it activates cAMP dependent protein kinase (an enzyme that phosphorylates proteins on serine and threoinie residues).
The response to NE is terminated by hydrolysis of cAMP to 5'-AMP and the removal of protein phosphate residues by protein phosphatases.
In Cardiac muscle cells, NE causes phosphorylation of voltage activated calcium channels, converting them to a form that can be opened by depolarization.

The phosphorylation of CA2+ channels by PKA is a result of direct binding of NE to calcium channels.

Protein phosphatases increase the phosphorylation of calcium channels by PKA.

The answer explains the cascade of events in the phosphorylation of CA2+ channels by PKA. The incorrect answers provide misleading statements that deviate from the actual process described in the correct answer.

Explanation

The answer explains the cascade of events in the phosphorylation of CA2+ channels by PKA. The incorrect answers provide misleading statements that deviate from the actual process described in the correct answer.

27. What does this result in?

It increases the probablitliy of voltage dependent activation.

It decreases the probability of voltage-dependent activation.

It has no effect on voltage-dependent activation.

It results in voltage-independent activation.

The correct answer explains the effect of the action, while the incorrect answers either state the opposite effect or a different unrelated effect.

Explanation

The correct answer explains the effect of the action, while the incorrect answers either state the opposite effect or a different unrelated effect.

28. What is activation of the beta-adrenergic receptors coupled to?

It's coupled to the decrease in potassium conductance through cAMP.

It's coupled to the increase in sodium conductance through cAMP.

It's coupled to the decrease in calcium conductance through cAMP.

It's coupled to the increase in calcium calcium conductance through cAMP.

Activation of beta-adrenergic receptors is known to stimulate an increase in calcium conductance through cAMP, not a decrease in calcium conductance or increases in sodium or potassium conductance.

Explanation

Activation of beta-adrenergic receptors is known to stimulate an increase in calcium conductance through cAMP, not a decrease in calcium conductance or increases in sodium or potassium conductance.

29. When binding of NE to beta-adrenergic receptors in heart cells occurs, how is G-protein effected?

Gs protein is inactivated and inhibits the enzyme adenylyl cyclase.

Gq protein is activated releasing its alpha and beta/gamma subunits which both bind to activate the enzyme adenylyl cyclase.

Gi protein is activated releasing its alpha and beta/gamma subunits which both bind to inhibit the enzyme adenylyl cyclase.

Gs protein is activated releasing its alpha and beta/gamma subunits which both bind to activate the enzyme adenylyl cyclase- the stimulatory effec is much greater of the alpha subunit than the beta/gamma subunit.

When NE binds to beta-adrenergic receptors in heart cells, the Gs protein is activated, releasing its alpha and beta/gamma subunits, leading to the activation of the enzyme adenylyl cyclase. This results in an increase in cAMP levels in the cell and a stimulatory effect on heart function. The incorrect answers provide misleading information about the effects of other G-proteins or incorrect outcomes.

Explanation

When NE binds to beta-adrenergic receptors in heart cells, the Gs protein is activated, releasing its alpha and beta/gamma subunits, leading to the activation of the enzyme adenylyl cyclase. This results in an increase in cAMP levels in the cell and a stimulatory effect on heart function. The incorrect answers provide misleading information about the effects of other G-proteins or incorrect outcomes.