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The impact of changing K+ concentrations on the membrane potential
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Tera_4979
#1 Posted : Saturday, August 08, 2020 12:24:00 AM
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Hi everyone,

I was wondering if someone could clarify how increasing and decreasing both extracellular K+ and intracellular K+ concentrations change the membrane potential. I keep finding contradictory information on this topic. It would also be extremely helpful if you could provide the same information for changing concentrations of Na+.

Thanks so much!
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INSTR_Katerina_102
#2 Posted : Saturday, August 08, 2020 3:23:09 AM
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Hi Tera,

Do you mean increasing/decreasing extracellular and intracellular K+ at the same time? Or like these kind of cases?

1. Increasing extracellular K+
2. Decreasing extracellular K+
3. Increasing intracellular K+
4. Decreasing intracellular K+

Please let me know,

Thanks,

Katt
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Tera_4979
#3 Posted : Tuesday, August 11, 2020 10:13:07 PM
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Hi Katt,

Thanks so much in your response! I was referring exactly to those four cases- sorry for the confusing wording. I was also wondering about the same responses for sodium, but I'm sure I'd be able to figure that out based on potassium.

All the best,
Tera
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INSTR_Katerina_102
#4 Posted : Wednesday, August 12, 2020 9:59:07 PM
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Hi Tera,

I've attached some mathematical reasoning to show the cases for K+ here: https://alumniubcca-my.s...uChscHBInlUSxw?e=yvpbTP

For this, I also found these questions historically confusing when I was learning this subject.

I think a lot of the confusion comes from the wording of questions like 125 in the EK exam for lecture 6, where the statement asks what will lower membrane potential -

When a question says lower membrane potential, a lot of the time they mean abolishing the gradient and therefore the potential - that is returning it to zero, not making it more negative. I personally don't like the wording as I feel it can get confusing (as different people refer to it in different ways in my experience), but I just recall that -/+ just represents the ion flow direction, and lower usually just means in terms of absolute value.

I hope this helps, please let me know if anything needs clarification.

Thanks,

Katt
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