If I bathe a squid axon in a fluid that has high sodium concentration , why does the duration of action potential decrease compared to a control experiment in low sodium bath but maintained at the same osmotic pressure with choline chloride? Why does the amplitude of action potential increase in the experimental set ?
In short- In the experiment, when the neurons are bathed in low sodium fluid but constant osmotic pressure, amplitude of action potential decreased, but duration of action potential increased.
I wanted to validate this with Nernst equation and/or GHK equation .
The increase is action potential amplitude with high extracellular sodium ( more sodium influx,more depolarization ? ) is intuitive? But again I am confused because the membrane is only slightly permeable to sodium such that increases in extracellular sodium won't really alter the membrane potential enough to generate an action potential.
Also how does the action potential duration decrease in high sodium ?
What should be done if I want to increase duration of action potential while keeping the axons in high sodium bath ?
- The duration of action potential is not the time to reach threshold voltage. It is the overall time the membrane stays depolarized.
- In other words, why are the axons slowly repolarized when bathed in low sodium concentration(and also maintained at constant osmotic pressure with choline chloride ) compared to high sodium bath axons that are rapidly repolarized ?
How do you think the answer would've changed if choline chloride was not used ?