I need some help on a science/medicine question right away, please?

[Th1onein]

Hi,

I know that if there are more solutes, such as salt (NaCl) in the extracellular environment, then the cell will absorb water, but will the cell absorb solutes (by whatever channel), when there is an increase in water inside of the cell?

For instance, water follows salt, but does salt follow water?

Please help.

[Richard Steele]

1. Not entirely sure that your question is properly worded...

But, as I am reading it, then YES.

You are surely asking this for a reason; could you give us more info?

[happyslug]

2. varies, depending on salt

For Example Salt Water Fish keep Salt out of their body, while fresh water fresh keep it in (as do land animals).

The liver is what regulate salt intake and output so you may want to look into the liver and other salt barriers.

[Redneck Socialist]

3. I believe the answer is no

If a cell is placed in a hypertonic solution (high concentration of solute) it will lose water.

If the cell is placed in a hypotonic solution (low concentration of solute) it will gain water.

http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm

[Th1onein]

6. I probably worded this wrong, let me try again.........

Okay....here we go....

Suppose you have an increased amount of glutathione inside of the cell; let's say it's trapped inside of the cell, because the membrane protein that normally transports it is mutated. That increased glutathione combines with hydrogen peroxide (H2O2) and you end up with oxidized glutathione and H2O (water), INSIDE of the cell.

Now, if you had that extra water inside of the cell, would the cell try to get the proper osmolarity by increasing, say, the activity of the sodium channels, and overabsorbing sodium? In turn, because sodium has a positive charge, you would not transport Cl- either.

Tell me if this is possible?

[Redneck Socialist]

11. Whoa...

we've moved way beyond my rather limited knowledge and recall of basic cellular biology so I'm going to flee back to GD and GD: P where I can more eloquently bullshit about politics. :hi: Sorry I couldn't be more help.

[Crunchy Frog]

4. I'm pretty sure that salt would not follow water into a cell.

Just trying to remember a little bit from the anatomy and physiology class that I took a couple of years ago. I seem to recall that water crosses the cell wall pretty spontaneously and by osmosis, but that salt only crosses the membrane by means of active transport, and its presence in the cell is pretty highly regulated. Therefore, it would not simply get absorbed into the cell by the presence of extra water.

That's what I seem to recall anyway. I may be wrong though.

[GaYellowDawg]

5. I'm not sure you've got this down pat.

I know that if there are more solutes, such as salt (NaCl) in the extracellular environment, then the cell will absorb water,

That's not correct. The reason is this:

If there are more solutes in water, there's a lower concentration of water. In other words, if there's a 5% salt solution, the other 95% is water. If there's a 15% salt solution, the other 85% is water. There's a lower concentration of water in the 15% salt solution.

Water, like everything else, diffuses from a high concentration to a low concentration. This would mean that water would go from the 5% salt solution to the 15% salt solution. If this diffusion happens across a membrane, then that's known as osmosis.

If there are more solutes in the extracellular environment, the cell loses water. See?

but will the cell absorb solutes (by whatever channel), when there is an increase in water inside of the cell?

For instance, water follows salt, but does salt follow water?

Please help.

First, there's something that you have to remember, which is that cell membranes are semipermeable. This means that some molecules can go right on through the membrane and others can't. Water is one of the molecules that can go through the cell membrane. That's why you can talk about water concentrations just going up/down at the inside/outside of the cell, because water passes through freely.

Some molecules can't go through the membrane, or go through it at different rates. This is independent of whether or not they dissolve in water.

So let's say that the membrane is completely permeable to a molecule; in other words, it lets the molecule pass back and forth through it freely. If that's the case, whether or not a molecule passes through is dependent on the concentrations inside and outside of the cell.

One molecule that can pass freely across membranes is CO2. So let's say that you take a cell that is 95% water with a .05% CO2 concentration and put it into a solution that is 75% water with a 0.5% CO2 concentration. What would happen would be that the cell would lose water but have its CO2 concentration raised.

If the membrane is semipermeable to a molecule, this transfer will happen but at a lower rate.

Does this help?

[mike_c]

7. depends on the permeability of the cell membrane for that...

...particular solute. Small ions tend to diffuse down their concentration gradients easier than larger molecules, for example. That is essentially how most animal excretory systems work at the cellular level-- active transport of some ion, like sodium, potassium, or urea, followed by passive osmosis of water (to dilute the potassium, etc), and then passive diffusion of other ions down their newly established concentration gradients. I've kind of mixed the details of exretory systems from several animals here, but the point is that the permeability of the epithelium lining the excretory tubules determines which molecules can "follow the water" by passive diffusion. The whole scheme saves great quantities of energy, because only the initial driving solute(s) needs to be actively transported.

[Th1onein]

9. Okay, maybe I've been thinking about this all wrong......

Let me ask you this:

Suppose you have a situation where there is an increased amount of water ALWAYS being generated INSIDE of the cell (such as in the case that I outlined previously with H2O2/glutathione and H2O)? Would you have chloride NOT being transported because of the overhydration of the cell? AND, then, an overabsorption of Na2+ (the law of electrical neutrality)?

[mike_c]

10. hmmm, interesting question....

I should preface this by stating up front that I'm not a physiologist, so I'm guessing. My first answer was in response to your OP, which was kind of vague on the details.

The first part of my guess is that it would depend at least partly on the type of cell involved, because the ion channels of different cells respond to different proximal stimuli. Now that I'm thinking about it with a cup of coffee in hand I don't think I can even hazard a good guess beyond that. The situation you've proposed results in both intensified osmotic gradients and (I think) decreased electro-chemical gradients across the plasma membrane. Maybe not reduced EC gradient strength if hyperproduction and oxidation of glutathione simply displaces negative charge from other amino acids and H2O2 where it would otherwise reside. You've probably figured out that part of the problem already, so I suspect you're ahead of me. Remember too that sodium-potassium pumps will presumably still be chugging away to maintain the normal Na-K gradient, and that their respective ion channels will still be responding to whatever they respond to in those cells. Presumably chloride ion will be pumped out to maintain the normal EC gradient as well, but the energy requirement would likely increase because the strength of the Cl osmotic gradient would increase, even if its EC voltage gradient does not. I just don't know whether you should expect the PM to respond actively to the modified osmotic and EC gradients. You need to run this by a cell physiologist, preferably one who knows a lot about membrane processes. I might very well have confused the issue further....

on edit: it's also not clear whether we're talking about the cascade of osmotic and EC perturbance that might result from glutathione overproduction and oxidation, or how cells might respond in order to maintain resting membrane gradients, or both. :shrug:

[Floogeldy]

8. No