Which of the following occurs in the presence of tetrodotoxin?

• A. Increased release of neurotransmitters at synapses
• B. Activation of potassium ion channels
• C. Enhanced muscle contraction
• D. Inhibition of sodium ion channels in nerve cells

Answer: (D)

Verified step by step guidance

1. Understand that tetrodotoxin is a potent neurotoxin that specifically targets nerve cells by blocking sodium ion channels.
2. Recall that sodium ion channels are essential for the initiation and propagation of action potentials in neurons, allowing sodium ions to enter the cell and depolarize the membrane.
3. Recognize that when tetrodotoxin blocks these sodium channels, it prevents the influx of sodium ions, thereby inhibiting the generation of action potentials.
4. Since action potentials are necessary for neurotransmitter release at synapses and muscle contraction, blocking sodium channels leads to decreased neurotransmitter release and muscle activity, not an increase.
5. Therefore, the key effect of tetrodotoxin is the inhibition of sodium ion channels in nerve cells, which explains why the other options (increased neurotransmitter release, activation of potassium channels, enhanced muscle contraction) do not occur.