sodium potassium pump question

[chiddler]

---

Members don't see this ad.

The Na+/K+ pump is a glycoprotein built into the membranes of all animal cells. It uses the energy of an ATP molecule to import two K+ ions into the cell and export three Na+ ions out of the cell. Which of the following will decrease the rate of ATP consumption by the Na+/K+ pump?

A. Placement of the cell into a hypertonic environment
B. Placement of the cell into a hypotonic environment
C. A defect in the sodium channel that allows more ions to leak into the cell
D. A defect in the potassium channel that facilitates leakage of potassium out of the cell

Answer: A.

Explanation not doing it for me.

Thanks.

 

[Dasypus]

It can't be C or D, because any defect in the channel that makes it work sub-optimally will make it burn more ATP to make up for the defect.

Down to A vs B, hypertonic vs hypotonic. What does the pump do, net? It spends an ATP to pump an ion out of the cell. If there is enough of an ion differential already outside the cell, the pump can run backwards, synthesizing ATP from ADP. That surely reduces ATP consumption. So A.

 

[DrRichand1]

I think this has to do with the resulting cell volume when placed in a hypertonic solution, the cell would crenate reducing it's volume and less Na/K+ pumping action would be needed to establish the desired RMP. If the cell had a larger volume it would take more pumping to establish RMP.

 

[chiddler]

It can't be C or D, because any defect in the channel that makes it work sub-optimally will make it burn more ATP to make up for the defect.

Down to A vs B, hypertonic vs hypotonic. What does the pump do, net? It spends an ATP to pump an ion out of the cell. If there is enough of an ion differential already outside the cell, the pump can run backwards, synthesizing ATP from ADP. That surely reduces ATP consumption. So A.

Thanks, but you're mistaken. It does both send ions in AND out of the cell.

 

[chiddler]

I think this has to do with the resulting cell volume when placed in a hypertonic solution, the cell would crenate reducing it's volume and less Na/K+ pumping action would be needed to establish the desired RMP. If the cell had a larger volume it would take more pumping to establish RMP.

can you please explain what you mean?

 

[cloak25]

Not sure if this helps, but wiki says that "when the cell begins to swell, this automatically activates the Na+-K+ pump, which moves still more ions to the exterior." Makes sense because in a hypotonic environment, the cell swells therefore activates the Na+/K+ pump = use more ATP. I guess the opposite happens for hypertonic environment? I'd also like a better explanation as to why A is correct.

 

[DrRichand1]

I guess the way i'm looking at it is the cell will have a smaller volume of cytoplasm to bring to resting membrane potential, since the cell shrunk it will not take as much Na/K Atpases to bring the cell to rmp because it's dealing with a smaller volume, therefore the cell wont need to run the bumps as much if it was trying to establish rpm of a huge cell.

don't know if this helps, but that's all i got.

 

[chiddler]

Hmm i think the question would at least suggested possibility. It seems too out there, you know?

But hey, if it is hyperosmotic, what does that say about osmolarity? As opposed to hypoosmotic conditions, the cell would have to pump a lot of ions out in order to become isotonic with the medium. When it is hyperosmotic, it can just absorb a lot of ions passively till it becomes isotonic! Therefore less Na/K pump action!

Can't take credit if this is correct though. The crappy explanation to the question, in addition to DrRichand1's suggestion, helped a lot.

 

[Morsetlis]

If you put an RBC into water (water is hypotonic to the cytosol), it swells, then lyses. I am sure you have seen this before:

Placing the cell into a hypertonic environment means the cell does not need to expend as much ATP to increase the tonicity of the environment (3 Na+ out, 2 K+ in).

You can think of the Na/K ATPase as pushing WATER out of the cell.

Clinical correlation: Pyruvate kinase deficiency leads to hemolytic anemia due to inability to form enough ATP in RBCs to drive the Na/K ATPase. Thus, water rushes into the cell, creating spherocytes (I thought it was echinocytes, I was wrong). Your RBCs should be biconcave discs, not spheres.

 

[MedPR]

Remember that water is almost always going to follow sodium. So as you pump out 3 sodiums, you are pumping out "3" waters. If you put the cell in a hypertonic environment, water is going to flow out passively and won't need the Na/K ATPase to help it as much.

 

[Morsetlis]

If you can answer these kinds of question, med school questions are a lot easier in comparison.

Of course, the difference is in memorization.

 

[MedPR]

If you can answer these kinds of question, med school questions are a lot easier in comparison.

Of course, the difference is in memorization.

Sometimes I read stuff out of FA and see if my girlfriend can answer what I'm talking about (She's studying for Step 1 now). The sheer volume that you guys need to memorize is insane.