Growth and membrane potential

[somasimple]

Hello everyone,

All living things have a growth cycle in which they gain mass and volume.
These elements are obviously and undoubtedly taken from the environment in which these creatures live.
Therefore, it is undeniable that the amount of potassium, for example, in the body increases during this growth cycle. It is undeniable that the amount of potassium in the cells increases during this growth cycle.
And yet,
The membrane potential (GHK equation) states that potassium continuously/constantly leaves the cell.

Is there not a contradiction here?

 

[BillTre]

No.
If there is a constant flow of K through the cell, and the amount of K diverted to stock newly generated cell volume is small in comparison, it will not be a problem.

Presumably something like this:
A cellular mechanism regulates pumping and transporting of K to maintain a fairly constant internal [K]. The K leaks in and gets pumped out. Some gets diverted to fill the new cell volumes because the regulatory mechanisms change pumping rate to keep [K] up.

 

[somasimple]

Thank you for this answer but the "no" seems... hasty.
What is the mechanism you are referring to?
The Na/K pump which is involved in only 5% of the membrane potential?
Moreover the K gradient is unfavorable =>4/140 to any inward diffusion, isn't it?

 

[BillTre]

I probably got the direction of the K backwards, but nevertheless modern cells will have mechanisms to maintain the [K] with in certain bounds in cells. Otherwise they would have problems.
You stated the cells are normally pumping K out, so it has to come from somewhere. Is it being pumped in for some reason?
Whatever,
there seems to be a flow of K through the cell. The inflows, outflows and the amounts stored in the cell have to make sense.

 

[somasimple]

I totally agree with you and that is the purpose of my question. The theory seems to be in complete contradiction with logic and facts.
The current theory imposes a constant outflow of potassium from the cell and a mechanism that could maintain a certain balance but only to a very small extent.
There is a problem with the assumption and the initial conditions.

 

[BillTre]

Could be.
Things often get twisted around.
What was your source of this information? It may be in conflict with other sources.
Also what kind of cells are you talking about? Sometimes different cells can do drastically different things.

 

[somasimple]

https://en.wikipedia.org/wiki/Goldman_equation
https://en.wikipedia.org/wiki/Membrane_potential

 

[Andy Resnick]

Hello everyone,

All living things have a growth cycle in which they gain mass and volume.
These elements are obviously and undoubtedly taken from the environment in which these creatures live.
Therefore, it is undeniable that the amount of potassium, for example, in the body increases during this growth cycle. It is undeniable that the amount of potassium in the cells increases during this growth cycle.
And yet,
The membrane potential (GHK equation) states that potassium continuously/constantly leaves the cell.

Is there not a contradiction here?

What is undeniable is that the concentration of K (and Na, and Cl, and...) stays constant.
What is undeniable is that NaKATPase exports Na and imports K to generate the membrane potential.

 

[jim mcnamara]

In support of @Andy Resnick's very nice answer

"The Na,K-ATPase classically serves as an ion pump creating an electrochemical gradient across the plasma membrane that is essential for transepithelial transport, nutrient uptake and membrane potential. In addition, Na,K-ATPase also functions as a receptor, a signal transducer and a cell adhesion molecule."
--
https://www.frontiersin.org › fcell.2015.00066

 

[somasimple]

Dear @Andy Resnick ,
Your answer could not be more straightforward.
But I don't think I'm disputing in any way that the various intracellular concentrations do not remain constant. I therefore agree with the first sentence of your answer in a perfectly indisputable way.

Concerning the second part, I preferred to go back to the works of Cristof Koch, Bertill Hille and even the Kandel. They are not as affirmative.

A simple look at Wikipedia could of course prove you right because it is indicated:
"The ion pump most relevant to the action potential is the sodium–potassium pump, which transports three sodium ions out of the cell and two potassium ions in.[11] As a consequence, the concentration of potassium ions K+ inside the neuron is roughly 20-fold larger than the outside concentration, whereas the sodium concentration outside is roughly ninefold larger than inside.[12][13] In a similar manner, other ions have different concentrations inside and outside the neuron, such as calcium, chloride and magnesium.[13]"

Unfortunately it seems that the authors of Wikipedia seem to rely on references that are at least six years older than the discovery of the famous pump. This is not very scientific writing.
In the same page, it is said above:

"The membrane potential in a cell derives ultimately from two factors: electrical force and diffusion. Electrical force arises from the mutual attraction between particles with opposite electrical charges (positive and negative) and the mutual repulsion between particles with the same type of charge (both positive or both negative). Diffusion arises from the statistical tendency of particles to redistribute from regions where they are highly concentrated to regions where the concentration is low."
This is the basis of the GHK equation where the permeability of K is 20 times that of Na.
This permeability seems to me very annoying for the pump...
This being said, I do not question the existence of the protein!

You see, Andy, contradictions remain!

 

[somasimple]

@jim mcnamara
Thank you for the reference.