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membrane potential

Anonymous Sat 14 Nov 14:29:37 2020 No.12340674 View Reply Original Report

Quoted By: >>12340920 >>12341091

I don't get it. I mean I get the Nernst and Goldman equations mathematically, but I can't relate it to reality.

Assume the following: A medium with equal amounts of K+ and Cl- ions (100 a.u. each) equally distributed. The medium is divided by a membrane only permeable for K+. There are ion transporters in the membrane that constantly transport K+ inside the cell so we reach a concentration ratio c_out/c_in of 5/95. The electrochemical gradient points outwards. K+ is flowing out as is transported back inside with an equal rate.

How is this supposed to give me a negative membrane potential?! There is more positive charge inside the cell.

Anonymous

Anonymous Sat 14 Nov 2020 16:09:02 No.12340920 Report

Quoted By: >>12342400

>>12340674
Tissues don't work like batteries.

The membrane potential is nothing more than a signal. In addition to the transporters maintaining the shit at those charges, something stimulates gated ion channels to open and they let the sodium flow in and potassium to flow out, Because of this flow the inside of the cell returns to be negative and voltage sensitive sodium channels make the thing repeat across the entire membrane.

Now the stimulus can be anything from activated Gprotein linked receptors which will eventually go to open calcium channels, to automatic slow repolarization calcium channels such as those in the heart, an electric current or physical damage to the membrane.

Anonymous

Anonymous Sat 14 Nov 2020 17:03:30 No.12341091 Report

Quoted By: >>12341132 >>12342400

>>12340674
You are forgetting about Na outside the cells

Anonymous

Anonymous Sat 14 Nov 2020 17:20:17 No.12341132 Report

Quoted By:

>>12341091
This. 3 sodium for every 2 potassium, leaving positive charge outside relative to inside.

Anonymous

Anonymous Sat 14 Nov 2020 23:18:31 No.12342400 Report

Quoted By: >>12343263

>>12340920

I am asking about the resting Potential.

>>12341091

Okay, there are 148mM of K+, 10mM of Na+, 4mM of Cl- inside and 5mM of K+, 142mM of Na+ and 103mM of Cl- outside. This gives me a net positive charge on both sides but the inside has more positive charge, so there should be a positive membrane potential.

Anonymous

Anonymous Sat 14 Nov 2020 23:21:25 No.12342409 Report

Quoted By:

His head is in the toilet lol toiletheaf

Anonymous

Anonymous Sun 15 Nov 2020 04:35:24 No.12343263 Report

Quoted By: >>12343530

>>12342400
anionic intracellular proteins that don't leave. Not rly sure if concentratin gradient ever overpowers electric gradient but sometin to thin abou

Anonymous

Anonymous Sun 15 Nov 2020 06:34:38 No.12343530 Report

Quoted By: >>12343672

>>12343263

I found examples where there would be still excess positive charge on the inside, eben with A- Ions taken into account

Anonymous

Anonymous Sun 15 Nov 2020 08:09:52 No.12343672 Report

Quoted By: >>12343733

>>12343530
K+ is in higher concentration inside cell generally, so the concentration gradient compels K to leave. Because there are always anions in the cells (proteins), these counterbalance the K from pozzing the cell, and when K leaves the cell gets even more neg. At a certain point, the cell gets so neg from K leaving towards its concentration gradient, that the negative electrical gradient building up inside the cell starts to oppose K’s affinity to leave towards its concentration gradient. At this point the ion is in electrochemical equilibrium. Basically because the concentration of K is higher inside the cell, it’s electrical gradient is going to be negative if the ion is at equilibrium. So I think I was sort of right in saying to think about the concentration gradient interacting with the electrical potential, because at equilibrium potential, those forces both equally cancel each other out, so no net change in ion concentration occurs. K is higher conc. in cell so it moves outward, making charge neg, which eventually opposes its own outward movement by drawing K back in via its electrical gradient. Na+, contrary to K, is higher conc. outside cell, so it flows in. This will make the resting potential less negative than K’s equilibrium potential, but still not a net positive resting potential (if cell was only permeable to Na the resting potential would be pos). That’s cuz membranes are more permeable to K than Na so K has an easier time leaving, making cell neg.

https://www.khanacademy.org/science/biology/human-biology/neuron-nervous-system/a/the-membrane-potential

Anonymous

Anonymous Sun 15 Nov 2020 08:48:15 No.12343733 Report

Quoted By: >>12343759

>>12343672

I read this kind of explanation literally 100 times.

As I said, I get the Equations, but if I approach the problem by purely counting charge distributions AT REST I get completely different results.

The fact that only very little ions have to cross the membrane for the potential to change confuses me then even more. There has to be a fuckload of charges moving across the membrane to go from uniform distribution to the one we can measure. Furthermore the outflow of K+ needs to be perfectly counterbalancef by KNaATPase er al. to Jeep the equilibrium, so there cannot be and net flow of ions, i. e. no current.

Anonymous

Anonymous Sun 15 Nov 2020 09:01:35 No.12343753 Report

Quoted By:

AND some explanations involve some gibberish about electroneutrality when this would obviously imply no potential difference...

Anonymous

Anonymous Sun 15 Nov 2020 09:04:19 No.12343759 Report

Quoted By:

>>12343733
I'm guessing the question just wants you to assume there are organic anions cuz that's only thing that would make it neg

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