A Hawaiian legend tells of a village that angered a shark god. In revenge, a "seaweed" began to grow in the tidepools that killed anyone who touched it. In fact, this "limu - make - o - Hana" - a zoanthid cnidarian - contains a palytoxin that locks the sodium - potassium pump open, allowing free flow of ions. If a villager suffers palytoxin poisoning, which way will the ions in his neurons flow?

Answer: Sodium ions will move from the exterior to the interior of the neuron, and Potassium ions will move from the interior to the exterior of the neuron.

Explanation:

Sodium-Potassium pumps in the neurons maintain a difference in electric potential to allow nerve impulses to happen. To do this, the pump extracts three Sodium ions from the neuron and places two Potassium ions (from the exterior of the neuron) inside the neuron.

As a result, normally the concentration of Sodium is very high outside the neuron, and so is the concentration of Potassium inside the cell. If the pump was open and ions could flow freely, they would tend to go from the most to the least concentrated region. This would result in Sodium moving inside the cell and Potassium moving out, impeding nerve impulses and killing the villager.