Lecture 14 : Toxins and Medicines

Question 1

Drug def

Answer 1

A chemical substance of known structure, other than a nutrient or an
essential dietary ingredient, which, when administered to a living
organism, produces a biological effect

Question 2

Medicines def

Answer 2

chemical substances, of known or
unknown composition, given to
achieve a therapeutic effect

Question 3

Non-medicinal drugs

Answer 3

Question 4

What is a toxin / poison

Answer 4

chemical substance, of known or unknown composition, given to
cause harm

Question 5

What is the step by step for neurotransmission?

Answer 5

1. Na+ influx initiates action potential
2. Ca2+ influx at pre synaptic bulb
3. Causes neurotransmitter to release by exocytosis
4. Neurotransmitter binds to target receptor
5. Neurotransmitter cleared by enzymes, uptake or diffusion
6. Neurotransmitter degraded and recycled
7. Signal processed in the target tissue

Question 6

Toxins that affect movement of ions involved in the direct ACTION POTENTIAL

Answer 6

Tetrodotoxin (TTX)
- Puffer fish
- Botox
- Useful if injected locally in small quantities, lethal poison if injected intravenously or ingested in large doses
- BLOCKS VOLTAGE GATED NA+ CHANNELS
- (some inhibitors of this channel are important in local anesthetic, eg. Lidocaine)
—
Apamin
- Bees
- Blocks K+ channels activated by Ca2+
- Increases excitability in sensory neurones’ axons
—
Omega-conotoxins
- Cone snail
- Block Ca2+ channels
- Used experimentally to study neurotransmission

Question 7

Toxins that affect exocytosis

Answer 7

Botulinum toxin
- Botox
- Clostridium botulinum (bacteria)
- Food poisoning (botulism)
- Useful if injected locally in small quantities, lethal poison if injected intravenously or ingested in large doses
- Blocks exocytosis
- Can be injected to decrease secretions at salivary or sweat glands
- Can be used cosmetically to decrease muscle tone
—
alpha-latrotoxin
- Black widow spider venom
- Reduces vesicle population
- Binds to protein found on neurones and inserts a pore to allow more calcium into the terminal, hence reducing vesicles crossing membrane by exocytosis

Question 8

Toxins that affect receptors

Answer 8

Atropine
- Berries of deadly nightshade
- Dilates pupils
- can inhibit salilva production
- Emergency treatment for slow hearts
- Muscarinic antagonist
—
Muscarine
- Poisonous fungi
- Activates muscarinic receptors
- ^ mediates parasympathetic responses
- Hence, heartrate is slowed, pupils constrict, airways relaxed, saliva increases

Question 9

Toxins affecting clearance of neurotransmitter

Answer 9

Question 10

Fox Glove

Answer 10

Question 11

Why do toxins exist

Answer 11