Hypokalemia

[methylethyl88]

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How does hypokalemia result in an increase in the excitability of nerve and muscle cells?

Shouldn't lower extracellular Ca++ result in decreased excitability or is it just assuming that a low extracellular concentration implies a high intracellular Ca++ concentration which would increase the availability of Ca++ for the troponin-tropomyosin complex?

 

[PiBond]

How does hypokalemia result in an increase in the excitability of nerve and muscle cells?

Shouldn't lower extracellular Ca++ result in decreased excitability or is it just assuming that a low extracellular concentration implies a high intracellular Ca++ concentration which would increase the availability of Ca++ for the troponin-tropomyosin complex?

remember that resting membrane potential of a cell interior is relative to the extracellular environment. therefore, if i take away positive charges (Ca2+ ions) from my ECF then i have made my cell interior "more positive" relative to my ECF than before. thus, less of stimulus is needed to reach threshold to open voltage gated channels which results in hyperexcitability.

 

[Charles_Carmichael]

Just so you know, hypokalemia is not referring to calcium levels. The -kal part is referring to potassium. So, hypokalemia is a decrease in potassium levels in the blood, not calcium. If you're talking about calcium, you use hypocalcemia or hypercalcemia.

 

[Drexon]

Just so you know, hypokalemia is not referring to calcium levels. The -kal part is referring to potassium. So, hypokalemia is a decrease in potassium levels in the blood, not calcium. If you're talking about calcium, you use hypocalcemia or hypercalcemia.

👍

Both author and second poster got mixed up. Hypokalemia = less than normal amount of potassium in the blood or outside of the cell. How does this relate to excitability of cells is as follows:
You decrease the relative concentrations of extracellular potassium in relation to intracellular potassium. This means more K+ inside relative to outside. If you have more "positive" inside than outside then your net result is that the resting membrane potential is higher or more positive relative to normal levels of potassium in the blood. Hence it's easier to excite.
I believe the second poster had it right except change calcium to potassium 😀

 

[PiBond]

👍

Both author and second poster got mixed up. Hypokalemia = less than normal amount of potassium in the blood or outside of the cell. How does this relate to excitability of cells is as follows:
You decrease the relative concentrations of extracellular potassium in relation to intracellular potassium. This means more K+ inside relative to outside. If you have more "positive" inside than outside then your net result is that the resting membrane potential is higher or more positive relative to normal levels of potassium in the blood. Hence it's easier to excite.
I believe the second poster had it right except change calcium to potassium 😀

actually, if we decrease ECF potassium then there's an increased concentration gradient leading to hyperpolarization (more K+ will leave the cells)--leading to muscle and neuronal tissues that become less excitable, not more, since they will have a lower RMP. it's a little different in the heart, but i won't go into that since it's beyond the mcat

i initially addressed the OP's calcium question and didn't address the misnomer.

 

[rls303]

actually, if we decrease ECF potassium then there's an increased concentration gradient leading to hyperpolarization (more K+ will leave the cells)--leading to muscle and neuronal tissues that become less excitable, not more, since they will have a lower RMP. it's a little different in the heart, but i won't go into that since it's beyond the mcat

i initially addressed the OP's calcium question and didn't address the misnomer.

Hi,
So if we see questions of these type, they simply mean what happens as a result of a hypokalemia....they wouldn't just ask us, is the muscle excitable at the instant the K+ concnetration is less in ECF?

Thanks

 

[PiBond]

Hi,
So if we see questions of these type, they simply mean what happens as a result of a hypokalemia....they wouldn't just ask us, is the muscle excitable at the instant the K+ concnetration is less in ECF?

Thanks

the MCAT would probably ask about the overall effects of hypokalemia on muscle excitability. however, at the moment that ECF K+ concentration decreases we will see an increase in K+ flux from the cell as a result of the increased concentration gradient (also recall that there are copious amounts of leak channels that allow potassium to leave). therefore, overtime this will lead to decreased muscle excitability as a result of hyperpolarization of the cells

 

[Drexon]

actually, if we decrease ECF potassium then there's an increased concentration gradient leading to hyperpolarization (more K+ will leave the cells)--leading to muscle and neuronal tissues that become less excitable, not more, since they will have a lower RMP. it's a little different in the heart, but i won't go into that since it's beyond the mcat

i initially addressed the OP's calcium question and didn't address the misnomer.

Haha ya i'm sorry it's been a while and i didnt think throughly :'(
Changing the extracellular concentration of potassium will change in the equilibrium potential for K so that the resting membrane potential of the cell will be lower than normal. Good eye PiBond

Best of luck on your test OP