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 Cardiac Action potential  



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Author15 Posts
  #1

when does voltage gated K channels begin to open?

a. Phase 0

b. Phase 1

c. Phase 2

c. Phase 3

d. Phase 4





  #2

c. Phase 3

remains open during phase 4




  #3

Right!


  #4

What is the reason for Phase1?


  #5

phase 1..slight repolarization due to closed Na channels and K conductance.

Now..BRS never mentioned whether these K channels are voltage gated or not..kaplan mentioned ungated channels are open always..and voltage gated channels are open phase 3 action potential onwards....depolarization is the signal for voltage gated K channels to close. and these channels remain closed in phase 2 too.

So, deducing from these, since ungated K channels are open all the time, then the slight reporization of Phase 1 is due to conductance through these channesl.

please correct me if i'm wrong..confused



  #6

no, it's some other channels, other than the ungated rectifier channels!


  #7

sad shaking head
What other channels ssprk sad(



  #8

don't remember where i read, but there are some K+ channels and also some Cl- channels tht play this role, more importanty these currents are not observed all over the conduction system and certainly not sensitive to block by anti-arrythmics, so not quite relevant!


  #9

Thanks mate


  #10

Fase 1 is when Na channels Close and K channel opens, then on Phase 2 Ca channels open slowly and produces the PLATEAU...Am i right nod



  #11

In the Kaplan Lectures they mentioned that there is always flow of K+ ions no matter what. Even if the voltage gated Ion channels donot open, the ungated will maintain the flow but at much slow speed. Dr. Dunn mentioned this very many times as he does in a very bold statement.


  #12

Kaplan lecture:

Every cell in the body has UNGATED K channel in the membrane; there will always be an efflux of K unless it is in equilibrium...



  #13

In kaplan.......

Phase 2......Voltage gated Ca channels are opened & voltage gated K channels are closed

So this slight repolarization may be due to these channels(Voltage gated K)......

Now it is not clearly written in kaplan that Voltage gated K channela are closed in Pahse O....when Na channels are open.......I think they are closed in pahse 2...



  #14

that slight repolarization is due to UNGATED K+ CHANNELS WHICH ARE ALWAYS OPEN. But the gated ones open in phase 3 which start closing in phase4 and close in phase 0, When Na+ plays role.
One secret is keep them seperate. Just byheart them.
Phase 0 is for Na
Phase 3 for K+
And there will be always flow of K= due to ungated which is very little. But does play role in slight repolarization. But I would still suggest you to refer some textbook too my friend coz I can wrong. I haven't checked yet. If find any diff. I shall mail ya.

SDK wrote:
In kaplan.......

Phase 2......Voltage gated Ca channels are opened & voltage gated K channels are closed

So this slight repolarization may be due to these channels(Voltage gated K)......

Now it is not clearly written in kaplan that Voltage gated K channela are closed in Pahse O....when Na channels are open.......I think they are closed in pahse 2...




  #15

In ganong.....

Phase 1 is due to closure of Na channels...






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