Hypokalemia and hyperkalemia

[SamarEsawy]

Changes in the serum concentration of ions, particularly potassium, can cause changes in SA nodal firing rate. Hyperkalemia induces bradycardia or can even stop SA nodal firing. Hypokalemia increases the rate of phase 4 depolarization and causes tachycardia. It apparently does this by decreasing gK during phase 4.

I don't understand this hypokalemia decreases the excitability of the cell so it would even take much time to depolarize it

thanks in advance

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[Packman2003]

[K+] is high in the cell, so when serum K+ decreases, this increases the concentration gradient and drives partial depolarization of the cell, bringing Em closer to threshold.

 

[CrouchingLiger]

Changes in the serum concentration of ions, particularly potassium, can cause changes in SA nodal firing rate. Hyperkalemia induces bradycardia or can even stop SA nodal firing. Hypokalemia increases the rate of phase 4 depolarization and causes tachycardia. It apparently does this by decreasing gK during phase 4.

I don't understand this hypokalemia decreases the excitability of the cell so it would even take much time to depolarize it

thanks in advance

What you have written seems accurate to me except for what I bolded. Hypokalemia seems to increase the excitability of the cell, which is why it leads to tachycardia as you wrote above. I'm not sure where you're getting that hypokalemia causes a decrease in excitability b/c that doesn't fit.

The way that I think of it (if you understand resting membrane potentials, etc.) is that with hypokalemia, there will also be less K+ within the cells, so the gradient for K+ going from inside the cell to outside is lower. This means that the resting potassium current (which is most responsible for the negative resting potential in the first place) is less, slightly increasing the resting membrane potential (closer to 0) and increasing excitability.

 

[SamarEsawy]

this increases the concentration gradient and drives partial depolarization

increasing concentration gradient leads to more K+ out of the cell thus the membrane potential becomes more negative and it becomes harder to excite the cell so how can hypokalemia cause tachycardia?
that's what is confusing me about it

The way that I think of it (if you understand resting membrane potentials, etc.) is that with hypokalemia, there will also be less K+ within the cells, so the gradient for K+ going from inside the cell to outside is lower. This means that the resting potassium current (which is most responsible for the negative resting potential in the first place) is less, slightly increasing the resting membrane potential (closer to 0) and increasing excitability.

hypokalemia means only decreasing concentration of K outside the cell which will lead to increasing concentration gradient

 

[SamarEsawy]

also that's why familial periodic hypokalemia causes paralysis due to decreased excitability of the cells

 

[SLC]

increasing concentration gradient leads to more K+ out of the cell thus the membrane potential becomes more negative and it becomes harder to excite the cell so how can hypokalemia cause tachycardia?
that's what is confusing me about it


hypokalemia means only decreasing concentration of K outside the cell which will lead to increasing concentration gradient

It's got everything to do with phaseIII of the pacemaker potential, depicted above. In phaseIII, there is a net potassium efflux.

If you increase [K+] outside the cell (hyperkalemia), you negatively impact phaseIII since there's a decreased gradient (intracellular-->extracellular).

If you decrease [K+] outside the cell (hypokalemia), you positively impact phaseIII since there's an increased gradient (intracellular-->extracellular).

 

[SamarEsawy]

I think it's all about delayed rectifying pot channel which starts closing at -60 so further negativity of the membrane will inhibit pot current through this channel..I think I get it right

 

[SLC]

I think it's all about delayed rectifying pot channel which starts closing at -60 so further negativity of the membrane will inhibit pot current through this channel..I think I get it right

Dude, you're overthinking this.

 

[SamarEsawy]

Dude, you're overthinking this.

may be but I read that the slope of phase 4 is increasing

 

[MCV 2016]

Dude, you're overthinking this.

This