BIOL 1F25 Lecture Notes - Lecture 25: Tetraodontidae, Ion Channel, Tetrodotoxin

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23 Jan 2017

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Jan. 23, 2017

Neuroscience - Lecture 5

Ion channels in the nerve cell membrane and neurotoxins that act on them

Ca2+ → charged molecule that is important for synaptic transmission

The nerve cell membrane had ION CHANNELS (pores that allow ions to move across

the membrane)

Ion channel gates open and close depending on various signals, to allow charges

through.

3 Main Properties:

1. Conduct ions (allow electricity to flow) Eg: calcium, potassium, sodium and

chloride

2. Selective. Eg: some pass mainly/ only sodium

3. Respond to different stimuli

Positive ions can cross the membrane together, negative ions can cross the membrane

together., but both positive as well as negative can’t cross the membrane together.

Respond to Stimuli:

Example:

1. Change in electrical potential across membrane

2. Ligand. Eg: transmitter or chemical

- Channels are activated by physical changes in the cell membrane

- Change in charge distribution across membrane

***When charge on the membrane changes, the gates open/ close***

- Different chemicals can activate or inactivate channels from outside of cell, or

inside of cell

- Ligands can stimulate both extracellular as well as intracellular activation

Neurotoxins - toxic substances that act on neurons. Many act on ion channels.

Many species of puffer fish release a very deadly toxin, known as Tetrodotoxin (TTX)!

TTX:

1. TTX - works by binding to the outside of voltage gated sodium channels

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Document Summary

Ion channels in the nerve cell membrane and neurotoxins that act on them. Ca2+ charged molecule that is important for synaptic transmission. The nerve cell membrane had ion channels (pores that allow ions to move across the membrane) Ion channel gates open and close depending on various signals, to allow charges through. 3 main properties: conduct ions (allow electricity to flow) eg: calcium, potassium, sodium and chloride, selective. Eg: some pass mainly/ only sodium: respond to different stimuli. Positive ions can cross the membrane together, negative ions can cross the membrane together. , but both positive as well as negative can"t cross the membrane together. Example: change in electrical potential across membrane, ligand. Channels are activated by physical changes in the cell membrane. ***when charge on the membrane changes, the gates open/ close*** Different chemicals can activate or inactivate channels from outside of cell, or inside of cell. Ligands can stimulate both extracellular as well as intracellular activation.

Related Questions

Bad Fish: The Case of Tetrodotoxin

Part I â Poisoned!

One evening during a trip to Indonesia to study the recent sightings of a coelacanth, Dr. Marshall Westwood from the Montana Technical Institute sat down to a meal of pufferfish and rice. Within an hour of returning to his hotel room, he felt numbness in his lips and tongue, which quickly spread to his face and neck. Before he could call the front desk, he began to feel pains in his stomach and throat, which produced feelings of nausea and eventually severe vomiting.

Fearing he had eaten some âbad fishâ for dinner, Dr. Westwood called a local hospital to describe his condition. The numbness in his lips and face made it almost impossible for him to communicate, but the hospital staff managed to at least understand the address he gave them and they sent an ambulance in response. As Dr. Westwood was rushed to the hospital, his breathing became increasingly difficult. In addition, he began to show signs of paralysis in his upper body and arms.

By the time the ambulance reached the hospital, Dr. Westwoodâs face and mouth were completely paralyzed and he had an irregular heartbeat. The physicians helped by keeping his airway open, administering drugs to bring his heart back to a normal rhythm, and putting a mixture of charcoal into his stomach, which would help absorb any chemicals that might still be left there.

Within a few hours, Dr. Westwoodâs condition improved and he was on his way to a full recovery. After discussing his case with his physician, he learned that he had probably been the victim of a pufferfish poisoning.

The active toxin in the tissues of this fish is a chemical called tetrodotoxin. Tetrodotoxin or (TTX) is in a class of chemicals known as neurotoxins due to the fact that it has its effects on nerve cells (neurons). Specifically, tetrodotoxin blocks voltage-gated sodium ion channels.

What follows is a series of questions relating to the basic biology of this case.

Answer the following questions about the case study:

1. How many different elements are contained in a molecule of tetrodotoxin? What are the names of these elements?

2. What is a voltage-gated sodium ion channel? What is it made of? What is its function?

3. Why do sodium ions need channels in order to move into and out of cells?

4. Describe the process involved in the movement of ions through these channels.

5. When nerve cells are at rest, there is an unequal amount of positive and negative charges on either side of a nerve cell membrane. This charge difference is called an electrical potential. Describe this âpotentialâ when the neuron is at rest (resting potential).

6. What is happening to the electrical potential of a neuron when it generates an action potential? What is the function of the action potential in neurons?

7. Describe the role of sodium ions and sodium channels in the action potential.

8. What would happen to a neuron if it were exposed to tetrodotoxin? Be specific regarding its effect on the ability of a neuron to communicate.

9. Now that you have addressed some of the basic biology of this case, explain why Dr. Westwood experienced numbness after eating the pufferfish meal.

10. Paralysis is a term used to describe the loss of function of muscle. If tetrodotoxinâs effect is on neurons, why did Dr. Westwood experience paralysis?

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BIOL 1F25 Lecture Notes - Lecture 25: Tetraodontidae, Ion Channel, Tetrodotoxin

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