Botulinus toxin causes paralysis. It binds to presynaptic sites at the motor end

Question

Botulinus toxin causes paralysis. It binds to presynaptic sites at the motor end plate (neuromuscular junction) and prevents the exocytotic release of transmitter from vesicles. Predict the consequences (increase, decrease, no change & explain why) of blocking the release of acetylcholine at the neuromuscular junction on the following: 1. Presynaptic resting potential 2. Presynaptic action potential amplitude 3. Presynaptic Ca2+ influx 4. Presynaptic transmitter release 5. Postsynaptic resting potential 6. Postsynaptic end plate potential 7. Postsynaptic action potential amplitude 8. Postsynaptic action potential frequency 9. Muscle contractile strength

Explanation / Answer

Botulinus toxin is secreted by the anerobic bacterium Clostridium botulinum, under anaerobic conditions. The toxin is a neurotoxin. The following are the actions of the toxin on the given conditions:

1. Presynaptic resting potential: Botulinum toxin inhibits the release of acetyl choline by inhibiting the enzyme, but does not affect the membrane permeability. Therefore, the potential remains unaltered.

2. Presynaptic action potential amplitude: Remains unaltered

3. Presynaptic Ca2+ flux: Remains unaltered

4. Presynaptic transmitter release: Transmitter release is inhibited by the toxin, and hence, it decreases

5. Postsynaptic resting potential: No effect of toxin on the post synaptic potential

6. Postsynaptic end plate potential: It decreases due to lack of stimulus in the absence of the neurotransmitter

7. Postsynaptic action potential amplitude: Remains unaltered

8. Postsynaptic action potential frequency: Decrease dur to the decreased end plate potential

9. Muscle contration strength: It decreases dur to lack of the neurotransmitter

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