Saxitoxin (STX) is one of the most potent neurotoxins known, and as a result, it is currently of great concern to bioterrorism experts. It is produced by dinoflagellates in the ocean and can be concentrated in the tissues of shellfish (mussels, scallops, and clams) that feed on these dinoflagellates. When STX-producing dinoflagellates are abundant, there is a "red tide," and people are warned to avoid shellfish. A neuron that is treated with STX shows the following characteristics:
(1) If you apply an extremely low dose of STX, you can still see an action potential, but
a. the threshold is much higher than normal
b. the amplitude of the action potential is reduced
(2) At higher doses, the neuron will not depolarize, no matter how much current you pass into it.
(3) Under voltage clamp conditions with Vm above threshold and higher doses of STX, you see only an outward current that appears normal.
Explain each of the observations (1), (2), and (3) and conclude with what you believe saxitoxin actually does to a neuron.
