3Na-1Ca exchanger?

[LovingItAll]

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I just got a Qbank question asking which transporter will move a net positive charge into the cytosol of a resting cardiac muscle cell during phase 4 of the action potential.

The answer was 3Na-1Ca exchanger.

Is this the exchanger that dig tries to slow by reducing the Na gradient?

 

[streetdoc]

I just got a Qbank question asking which transporter will move a net positive charge into the cytosol of a resting cardiac muscle cell during phase 4 of the action potential.

The answer was 3Na-1Ca exchanger.

Is this the exchanger that dig tries to slow by reducing the Na gradient?

i had that one too. it is NOT the Dig site since that is the ATPase that it will block. i think, THINK, they were going for a pure charge type thing. i got it wrong and read the expllination and was a bit more confused...i know that didn't help you much, but hey, at least both were confused.
streetdoc

 

[ucbdancn00]

the answer may lie in the fact that there is a "window current" of Na+ during phase four (contributes to the funny current in SA/AV)

hope this helps..

ucb

 

[LovingItAll]

i had that one too. it is NOT the Dig site since that is the ATPase that it will block. i think, THINK, they were going for a pure charge type thing. i got it wrong and read the expllination and was a bit more confused...i know that didn't help you much, but hey, at least both were confused.
streetdoc

Confusion, like misery, always enjoys good company. 🙂

Just to clarify, I wasn't suggesting that dig works on a Na-Ca exchanger directly. We agree that dig blocks the Na-K ATPase, causing a higher intracellular [Na], which in turn reduces the Na gradient driving a Na-Ca exchanger, causing an increase in [Ca] since less Ca is exchanged out.

So maybe this Na-Ca exchanger is what the Qbank question was referring to.

Oh well, let's all agree that if this is on Step 1, we all answer C.

 

[LovingItAll]

the answer may lie in the fact that there is a "window current" of Na+ during phase four (contributes to the funny current in SA/AV)

hope this helps..

ucb

ouch - never heard of it.

 

[HiddenTruth]

the answer may lie in the fact that there is a "window current" of Na+ during phase four (contributes to the funny current in SA/AV)

hope this helps..

ucb

I think the OP mentioned muscle cell. I don't think the window current is present in the atr/ventr mm fibers.

 

[Ramoray]

Is it jsut me or maybe im reading the question wrong but i think its just a simple concept with all you have to realize is phase 4 has followed the AP and contraction of the ventricle and is now resting. At this point the cell is still recovering from the AP as far as calcium goes and the only way the Ca will go unless it is phase 0,1 or 2 is out or into the SR. So the 3 Na to 1 Ca to me you dont have to remember which pump it is you just have to realize calcium would be on its way out so that must mean the transporter is working with the 3Nas going in and pumping the Ca out which obviously gives you a net positive charge inside. Seems like a confusing question testing a really simple concept but then again i didnt read the whole question stem or answers so i might be misreading.

 

[HiddenTruth]

Since when did phase 4 of resting cardiac muscle fibers start pumping Na or Ca? This questions makes no sense.

 

[ucbdancn00]

Since when did phase 4 of resting cardiac muscle fibers start pumping Na or Ca? This questions makes no sense.

exactly...which is why i thought it may have something to do with the window current...

hard to say though, we don't have the full question...

ucb

 

[Ramoray]

ANy phase after an action potential the cell will be working on extruding every last bit of CA. Phases are man made, it is a whole constant thing and up until the next phase 0, the cell is extruding all the last Ca in the cell it can including phase 4, allbeit less than direct recovery in phase 2, 3 etc