Help with the EK Biology question!!

[umermus]

I have trouble understanding the concept the EK book presents in their explanation for Lecture question # 83 from chapter 4. I was wondering if it one of those Errata that people keep on mentioning. Any help would be appreciated.

For those who don't have the EK books, I am posting the question:

83. A cell membrane is very slightly permeable to potassium ions. If a membrane were to become impermeable to potassium ions, the neuron's resting membrane potential would:

A. become more positive because potassium ion conc. would increase inside the neuron.
B. become more positive because potassium ion conc. would increase outside the neuron.
C. become more negative because potassium ion conc. would increase inside the neuron.
D. become more negative because potassium ion conc. would increase outside the neuron.

Thanks

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[iA-MD2013]

A
The Na/K ATPase along with the K leak channels is responsible for a cell's resting membrane potential. The Na/K ATPase pumps 3 Na ions out of the cell and 2 K into the cell (while using up one ATP). The leak channels cause the K to leak back out of the cell. This causes a polarization of the cell with a net negative charge inside the cell and a positive charge outside (-70mV). This should make sense because we keep pumping positive charges out of the cell.
Ok, so if we remove the K leak channels: We are still pumping 3 Na out of the cell and 2 K into the cell. But, now, the K is stuck in the cell. It can't leave through the channels. This causes a much smaller negative charge to reside in the cell (or a more positive charge). This will result in a more positive membrane potential because the conc of K has increased inside the cell (neuron). So, the answer would be A.
Hope that helped....

 

[umermus]

thanks a lot for the reply. I was reading the membrane being impermeable to the K ions as inactivity of Na/K channels which is not the case. Thanks again for the help.

 

[iA-MD2013]

ahhh i see what you were thinking. yes, that would make things incredibly confusing.

 

[J ROD]

Not that it matters, but I concur.

A

 

[blastula]

Another way to look at this is to think about the potential curve. Starting from resting potential -70mV, inward movement of Na+ down its gradient makes the potential more positive up to +30mV. Outward movement of K+ down its gradient makes it more negative bringing it back down to resting. If K+ could not flow out of the cell down its natural gradient the potential would remain positive.