Question

Tetrodotoxin, an extremely potent poison produced by pufferfish, binds tightly to voltage-gated Na channels and blocks the flow of Na ions but does not affect K or Cl ion channels. So which phase of AP does it block?

Answer 1

Tetrodotoxin blocks the flow of sodium ions by binding tightly to voltage-gated sodium channels, affecting the depolarization phase of the action potential.

Step-by-step explanation:

Tetrodotoxin blocks the flow of sodium ions by binding tightly to voltage-gated sodium channels. This means that it affects the phase of the action potential where sodium ions normally flow into the cell, which is the depolarization phase. During this phase, the membrane potential becomes more positive as sodium ions enter the cell through the open voltage-gated sodium channels. Tetrodotoxin prevents this influx of sodium ions, leading to the inhibition of the action potential.