1 of 41

Bad Fish, Bad Bird

Kristi Hannam, SUNY-Geneseo

Adapted from a case by James A. Hewlett

2 of 41

One evening during a trip to Indonesia to study the recent sightings of a coelacanth, Dr. Marshall Westwood from the Montana Technical Institute ate a meal of pufferfish.

2

Local Cuisine

3 of 41

Within an hour of returning to his hotel room, he:�

3

  • felt numbness in his lips and tongue
    • which quickly spread to his face and neck.
  • began to feel pains in his stomach and throat
    • which produced feelings of nausea and eventually severe vomiting.

4 of 41

Dr. Westwood called a local hospital. Numbness in his lips and face made it almost impossible for him to communicate, but the hospital staff sent an ambulance.

4

5 of 41

As Dr. Westwood was rushed to the hospital, he had:

    • trouble breathing;
    • signs of paralysis in his upper body and arms.

5

6 of 41

The Physicians…

  • kept his airway open.
  • administered drugs to bring his heart back to a normal rhythm.
  • put a mixture of charcoal into his stomach to help absorb any chemicals that might still be there.

6

7 of 41

Within a few hours, Dr. Westwood's condition improved and he was on his way to a full recovery. 

​

​

7

After discussing his case with his physician, he learned that he had probably been the victim of a pufferfish poisoning.

8 of 41

POISONED!

  • The active toxin in the tissues of this fish is a chemical called tetrodotoxin. 
  • Tetrodotoxin is a neurotoxin - it affects nerve cells (neurons). 
  • Specifically, tetrodotoxin blocks voltage-gated sodium ion channels.

8

9 of 41

CQ#1: The symptoms Dr. Westwood suffered included all of the following EXCEPT:

A. Fever and chills

B. Numbness

C. Paralysis

D. Difficulty breathing

E. Nausea and vomiting

9

10 of 41

CQ#2: According to what you know so far, voltage-gated sodium ion channels are found in:

A. Cells of pufferfish

B. All living cells

C. Epithelial cells

D. Nerve cells

E. None of the above

10

11 of 41

CQ#3: If tetrodotoxin (TXX) blocks voltage-gated sodium ion channels, which part of the action potential graph would be impacted?

A. Part A

B. Part B

C. Part C

D. Part D

E. Part E

11

TIME

Membrane Voltage (mV)

-70

-55

0

30

A

B

C

D

E

12 of 41

The Charge Across Cell Membranes

  • All cells have an electrical potential difference across their plasma membrane.
    • Called a MEMBRANE POTENTIAL

​

  • The cell’s inside is negative relative to the outside.
  • Sodium (Na+) potassium (K+) and large anions (A-) are important in maintaining the membrane potential.

12

Extracellular

Intracellular

Neuron Cell Membrane

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

K+

K+

K+

K+

K+

K+

K+

K+

K+

K+

K+

K+

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

13 of 41

The Charge Across Cell Membranes

  • The interior of a cell’s membrane is hydrophobic and repels ions and molecules with charge.

​

  • In order for an ion to cross the membrane, it must use a channel that facilitates its movement.

​

13

Extracellular

Intracellular

Neuron Cell Membrane

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

K+

K+

K+

K+

K+

K+

K+

K+

K+

K+

K+

K+

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

K+

Na+

14 of 41

The Charge Across Cell Membranes

  • Passive ion channels allow diffusion of K+ and Na+ across the membrane.

​

  • There are MANY passive K+ channels and very few Na+ channels making the membrane 100x more permeable to K+ than Na+.

14

Extracellular

Intracellular

Neuron Cell Membrane

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

K+

K+

K+

K+

K+

K+

K+

K+

K+

K+

K+

K+

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

A-

K+

K+

K+

K+

Na+

15 of 41

CQ#4: The movement of charged ions based on concentration gradients when the nerve is at rest….

Examine the figure to the right

and predict the direction Na+ and

K+ will move via diffusion based

on concentration if all ion

channels are open.

​

    • Both Na+ and K+ will move OUT of the cell.

B. Both Na+ and K+ will move INTO the cell.

C. Na+ will move OUT and K+ will move INTO the cell.

D. Na+ will move IN and K+ will move OUT of the cell.

E. Neither Na+ nor K+ will move across the cell membrane via diffusion.

15

Extracellular

Intracellular

Neuron Cell Membrane

Na+

150mM

​

Na+

15mM

K+

150mM

K+

5mM

A-

110mM

16 of 41

Resting Potential in Neurons

Diffusion of K+ (and less Na+) leads to a separation of charges across the membrane, and the resting potential.

​

    • Remember: There are MANY K+ and very few Na+ channels, thus membrane permeability is 100x for K+ than Na+.
    • Movement of K+ increases the positive charge outside the membrane relative to the inside.

16

Thus an ELECTRICAL gradient is formed that

can also influence ion flow.

​

17 of 41

Maintaining the Resting Potential: the Sodium-Potassium Pump

  • The pump moves three sodium (Na+) ions out of the cell for every two potassium (K+) ions that it brings in.
  • This helps the cell maintain a separation of charges.

17

18 of 41

Resting Potential

18

TIME

Membrane Voltage (mV)

-70

-55

0

30

At Resting Potential, the inside of the neuron is negative relative to the outside and is thus polarized. (-70Mv).

​

19 of 41

Action Potentials: How Nerves Communicate

  • Neurons are specialized to use changes in membrane potential for fast communication- called an ACTION POTENTIAL.
  • Neurons have special gated ion channels, that open or close in response to stimuli.
  • Membrane potential may change in response to stimuli that open or close those channels.

​

19

20 of 41

CQ#5: When a neuron is stimulated, the area of the membrane at the point of stimulation becomes more permeable to Na+.

If a cell starts at resting potential (-70mv), and then is stimulated:

​

  1. The membrane voltage will become < -70mV, because Na+ will move OUT of the cell
  2. The membrane voltage will become >-70mV, because Na+ will move OUT of the cell.
  3. The membrane voltage will become < -70mV because Na+ will move INTO the cell
  4. The membrane voltage will become >-70mV because Na+ will move INTO the cell.

20

TIME

Membrane Voltage (mV)

-70

-55

0

30

21 of 41

Action Potential: Part 1

  • For an action potential (nerve firing) to occur, the cell membrane potential must reach a threshold value of …

~ -55mV

  • When this threshold is reached, the voltage-gated Na+ channels open, allowing more Na+ to diffuse rapidly into the cell.
    • DEPOLARIZATION

21

TIME

Membrane Voltage (mV)

-70

-55

0

30

22 of 41

CQ#6: At the peak of the action potential, Na+ voltage-gated channels close, and K+ voltage-gated channels open in response to positive membrane potential. To return the cell to its negative resting potential quickly:

  1. K+ will diffuse along its concentration gradient INTO the cell.
  2. K+ will diffuse along its concentration gradient OUT of the cell.
  3. Na+ will reverse its direction of diffusion OUT of the cell.
  4. The sodium-potassium pump will move Na+ OUT of the cell and K+ INTO the cell.
  5. None of the above would return the cell to its negative resting potential quickly.

22

TIME

Membrane Voltage (mV)

-70

-55

0

30

23 of 41

CQ#7: Dr. Westwood ate a meal of pufferfish and rice. As a result, he was a victim of pufferfish poisoning that caused his life-threatening symptoms of numbness, paralysis, irregular heartbeat, and difficulty breathing. Tetrodotoxin (TXX), found in pufferfish flesh, is a molecule that:

  1. Causes the flesh of pufferfish to go bad.
  2. Causes an incurable illness in humans.
  3. Blocks voltage-gated sodium ion channels.
  4. Blocks neurotoxins.
  5. Affects the immune system.

23

24 of 41

CQ#8: If tetrodotoxin (TXX) blocks voltage-gated sodium ion channels, which part of the action potential would be impacted?

  1. Part A
  2. Part B
  3. Part C
  4. Part D
  5. Part E

24

TIME

Membrane Voltage (mV)

-70

-55

0

30

A

B

C

D

E

25 of 41

CQ#9: Dr. Westwood experienced numbness after eating the pufferfish meal because TXX causes:

  1. Motor neurons to fire continuously, overloading the brain with signals, resulting in numbness.
  2. Motor neurons to stop firing, preventing communication with the brain, resulting in numbness.
  3. Sensory neurons to stop firing preventing communication with the brain, resulting in numbness.
  4. Sensory neurons to fire continuously, overloading the brain with signals, resulting in numbness.
  5. None of the above explain why Dr. Westwood experienced numbness after his pufferfish meal.

25

26 of 41

CQ#10: Why did Dr. Westwood experience paralysis after eating the pufferfish meal?

  1. TXX causes motor neurons to fire continuously, overloading the brain with signals, resulting in paralysis.
  2. TXX causes motor neurons to stop firing, preventing communication with the muscles, resulting in paralysis.
  3. TXX causes sensory neurons to stop firing preventing communication with the brain, resulting in paralysis.
  4. TXX causes sensory neurons to fire continuously, overloading the brain with signals, resulting in paralysis.
  5. None of the above explain why Dr. Westwood experienced numbness after his pufferfish meal.

26

27 of 41

After recovering from his TTX poisoning, Dr. Marshall Westwood took a vacation. An avid birder, he went to Papua New Guinea with Bill Whitlatch, an ornithologist and friend.

27

28 of 41

Three days into their trip, Bill netted a bird with an orange body and black wings and head.

​

Dr. Westwood was very curious and looked closely at the bird. 

28

29 of 41

After handling the bird and later touching his mouth with his hand, Dr. Westwood noticed that his fingers and lips were going numb.  His mind immediately flashed back to the disastrous trip to Indonesia and he began to panic.  Luckily, the symptoms faded.

29

30 of 41

His friend Bill used a key to identify the animal as a pitohui.  The pitohui are small, social songbirds that live in Papua New Guinea. 

​

Their encounter was the first time any scientist had realized the birds were toxic.

30

31 of 41

Dr. Westwood collected feather and tissue samples to bring back to the lab.  After returning to Montana, he isolated the toxic compound that he was active in the feathers of the pitohui.  It appeared that the active ingredient was a homobatrachotoxin. 

31

32 of 41

  • Homobatrachotoxin is a steroidal alkaloid that is similar to batrachotoxin, the toxic principle of the Central American poison arrow frog Phyllobates aurotaenia. 
  • Batrachotoxin and homobatrachotoxin are both known to act on voltage-sensitive sodium channels in excitable tissues.

32

33 of 41

CQ#11: What symptoms did Dr. Westwood experience after both his pufferfish meal and after handling the new bird species?

  1. Nausea
  2. Numbness
  3. Paralysis
  4. Difficulty breathing
  5. More than one of the above

33

34 of 41

CQ#12: The toxin found in the bird feathers:

  1. Is used by the birds to deter predators.
  2. Is found in birds that have eaten poison arrow frogs.
  3. Is the same toxin found in pufferfish flesh.
  4. Affects voltage sensitive ion channels.
  5. Affects voltage sensitive potassium channels.

34

35 of 41

Dr. Westwood has asked you to help elucidate the mechanism of action of this new toxic compound.

  • In your first experiment, you generated action potentials in axons of large neurons obtained from squid in the presence of this new toxin. You found after depolarizing, the membrane potential remained positive for an extended length of time and the repolarization was often extremely delayed.

​

  • Draw a graph showing membrane potential vs. time to illustrate this effect.

35

36 of 41

CQ#13: Choose the graph below that most closely matches the graph you just created:

36

-70

-55

0

30

Membrane potential (mV)

Time

-70

-55

0

30

Membrane potential (mV)

Time

-70

-55

0

30

Membrane potential (mV)

Time

-70

-55

0

30

Membrane potential (mV)

Time

A

B

C

D

37 of 41

CQ#14: You experiment with higher concentrations of toxin and find cases when the cell could not repolarize at all or, if it began to repolarize, it immediately depolarized again. This tells you that the toxin:

  1. Prevents voltage-gated K+ channels from opening.
  2. Increases the speed that Na+ ion channels open.
  3. Prevents Na+ ion channels from closing.
  4. Makes Na+ ion channels close too soon.
  5. Doesn’t affect the Na+ ion channels at all, it affects the sodium-potassium pump instead.

37

38 of 41

CQ#15: In this case study you have learned:

  1. Poisons that affect nerves interfere with ion channels.
  2. Never eat pufferfish.
  3. Science depends on accidental discoveries.
  4. Electrical potentials across membranes can be manipulated with ion channels.
  5. None of the above.

39 of 41

Slide Credits

Slide 1

Description: Pufferfish (Takifugu rubripes) swimming in tank.

Author: Chris 73, http://en.wikipedia.org/wiki/User:Chris_73

Source: Wikimedia Commons, http://commons.wikimedia.org/wiki/Image:Fugu_in_Tank.jpg

Clearance: Licensed according to terms of Creative Commons Attribution-Share Alike 3.0 Unported.

​

Slide 2 —Top right

Description: Tray with six pufferfish (Takifugu rubripes).

Author: Chris 73, http://en.wikipedia.org/wiki/User:Chris_73

Source: Wikimedia Commons, http://commons.wikimedia.org/wiki/Image:Fugu.Tsukiji.CR.jpg

Clearance: Licensed according to terms of Creative Commons Attribution-Share Alike 3.0 Unported.

​

Slide 2 —Bottom right

Description: Sushi plate.

Author: Evil Julia, http://www.flickr.com/photos/evil_julia

Source: Flickr, http://www.flickr.com/photos/evil_julia/124972796/

Clearance: Licensed according to terms of Creative Commons Attribution-Share Alike 2.0 Generic.

​

Slide 3

Description: Hotel room.

Author: Derek Jensen

Source: Wikimedia Commons, http://commons.wikimedia.org/wiki/File:Hotel-room-renaissance-columbus-ohio.jpg

Clearance: Released into the public domain by the image author.

​

Slide 4

Description: Phone.

Author: ©Benjamin Mercer

Source: Fotolia.com

Clearance: Licensed, royalty free image.

​

40 of 41

Slide 5

Description: Ambulance.

Author: ©Thaut Images

Source: Fotolia.com

Clearance: Licensed, royalty free image.

​

Slide 6

Description: Surgeons.

Author: ©Andres Rodriguez

Source: Fotolia.com

Clearance: Licensed, royalty free image.

​

Slide 7

Description: Puffer fish.

Author: Mila Zinkova

Source: Wikimedia, http://commons.wikimedia.org/wiki/File:Puffer_Fish_DSC01257.JPG

Clearance: Licensed according to terms of Creative Commons Attribution-Share Alike 3.0 Unported.

​

Slide 8

Description: Tetrodotoxin molecular structure.

Author: Ben Mills

Source: Wikimedia, http://commons.wikimedia.org/wiki/Image:Tetrodotoxin-3D-balls.png

Clearance: Released into the public domain by the image author.

​

Slide 11 , Slide 18 , Slide 20 , Slide 21 , Slide 22 , Slide 24 , and Slide 36

Description: Various graphs.

Author: Kristina M. Hannam, Department of Biology, SUNY Geneseo

Clearance: Used with permission of author.

​

Slide 12 , Slide 13 , Slide 14 , and Slide 15

Description: Images depicting membrane potential in nerve cell with ion concentrations.

Author: Kristina M. Hannam, Department of Biology, SUNY Geneseo

Clearance: Used with permission of author.

​

41 of 41

Slide 16 and Slide 19

Description: Golgi stained pyramidal neuron in the hippocampus of an epileptic patient. 40 times magnification.

Author: MethoxyRoxy

Source: Wikimedia, http://commons.wikimedia.org/wiki/Image:Pyramidal_hippocampal_neuron_40x.jpg

Clearance: Licensed according to terms of Creative Commons Attribution-Share Alike 2.5 Generic.

​

Slide 17

Description: Sodium-potassium pump.

Author: LadyofHats, Mariana Ruiz Villarreal

Source: Wikimedia Commons, http://commons.wikimedia.org/wiki/Image:Scheme_sodium-potassium_pump-en.svg

Clearance: Released into the public domain by the image author.

​

Slide 27

Description: Map of Papua New Guinea.

Author: User:Vardion

Source: Wikimedia Commons, http://commons.wikimedia.org/wiki/File:LocationPapuaNewGuinea.svg

Clearance: Licensed according to terms of Creative Commons Attribution-Share Alike 3.0 Unported.

​

Slide 28 and Slide 30

Description: Hooded Pitohui, Pitohui dichrous.

Author: markaharper1

Source: Flickr, http://www.flickr.com/photos/16420772@N07/2884896043/

Clearance: Licensed according to terms of Creative Commons Attribution-Share Alike 2.0 Generic.

​

Slide 32

Description: A kokoe dart frog (Phyllobates aurotaenia) staring at an African violet.

Author: Onagro

Source: Wikimedia Commons, http://commons.wikimedia.org/wiki/File:Phyllobates_Aurotaenia_Red_%26_Violets.jpg

Clearance: Licensed according to terms of Creative Commons Attribution-Share Alike 3.0 Unported.