Question
A 27-year-old man is brought to the emergency department because of weakness, headache, and vomiting for 40 minutes. He is an amateur chef and his symptoms started 10 minutes after he ingested pufferfish that he had prepared. On arrival, he is lethargic. His temperature is 37°C (98.6°F), pulse is 120/min, respirations are 8/min, and blood pressure is 92/64 mm Hg. He is intubated and mechanical ventilation is begun. Intravenous fluid resuscitation is started. The cause of this patient’s condition exerts its effect by which of the following mechanisms of action?
| A. |
Decrease in cell membrane permeability to sodium ions
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| B. |
Increase in cell membrane permeability to chloride ions
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| C. |
Decrease in cell membrane permeability to potassium ions
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| D. |
Increase in cell membrane permeability to calcium ions
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Show Answer
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Correct Answer � A
Explanation
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Answer A) Decrease in cell membrane permeability to sodium ions
Ingestion of improperly prepared pufferfish can result in intoxication with tetrodotoxin, a potentially life-threatening toxin, which is found primarily in the fish’s ovaries and liver.
Decrease in cell membrane permeability to sodium ions
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Tetrodotoxin blocks voltage-gated sodium channels, thereby inhibiting the propagation of action potential in autonomic, motor, and sensory nerve cells.
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This inhibition initially causes headache, vomiting, and tingling of the tongue and lips; the condition can then progress to ataxia, generalized weakness, paralysis, and sometimes even respiratory and cardiovascular failure.
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Treatment is supportive, and mechanical ventilation may be needed.
Increase in cell membrane permeability to chloride ions
Drugs that increase the permeability of the cell membrane to chloride ions are used to treat helminth infections (e.g., ivermectin) and constipation (e.g., lubiprostone). Tetrodotoxin does not target chloride
Decrease in cell membrane permeability to potassium ions
A decrease in cell membrane permeability to potassium ions is the mechanism of dendrotoxin, which is released, for example, by the mamba snake. Potassium channels are also targeted by some antidiabetic drugs (e.g., sulfonylurea and repaglinide) and antiarrhythmic drugs (e.g., amiodarone and sotalol). Tetrodotoxin does not target potassium channels.
Increase in cell membrane permeability to calcium ions
Voltage-gated L-type Ca2+ channels play an important role in the action potential of cardiomyocytes and arterial smooth muscle cells. They are activated by antihelminthic drugs (e.g., praziquantel), not by tetrodotoxin.
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