Respiratory exchanges: is Chloride Shift in RBCs an example of ACTIVE or PASSIVE transport?

[greenmatter]

Hello there, I'm here again. 🙂

I was wondering if "chloride exchangers" in Red Blood Cells are an example of active transport or not.

In particular, to make things easier, let's say that I'm only focusing on what happens in systemic capillaries.

Since on my books I couldn't find anything, I searched for some informations on the internet and I got this:

http://books.google.it/books?id=e6f...v=onepage&q=is chloride shift passive&f=false

Have a look at pages 252-253. Anyway, I'm writing down the "important" part for you, at page 253:

" Bicarbonate moves against its concentration gradient: erythrocyte [HCO3-] is about 15mM, while plasma is 24mM. Chloride moves down its concentration gradient. This ACTIVE transport is facilitated by the Band3 anion exchanger protein".

So, it looks an ACTIVE process to me.
__________

However, here:

http://oregonstate.edu/dept/biochem/hhmi/hhmiclasses/biochem/lectnoteskga/2kfeb02lecturenotes.html

...it's depicted as a facilitated diffusion mechanism.

__________

I believe that this is an active process, facilitated in some way.

Probably this is way too technical, but I'm really wondering: is this an active or passive transport?

The fact is: if it was a primary active transport, we'd have ATP hydrolysis (and there isn't).
If it was secondary active transport, there would have been some other coupled protein pumping chloride outside, in order to mantain a certain gradient (for instance) - and neither is there.

So, what do you think?

Many thanks for reading!

---

Members don't see this ad.

 

[worldbeater]

I would think it is passive transport.

If your talking about the chloride shift that occurs in the proximal convoluted tubule, it is an exchange of 1 molecule of HCO3- in the PCT cell with the Cl- from the serum. No ATPase pump is being used, because nothing is being pushed against it's concentration gradient.

 

[greenmatter]

Many thanks for your answer.

The problem is that, according to the first link (which redirects to a book), [HCO3-] in plasma is higher than [HCO3-] in red blood cell.

By assuming that this is NOT at all a primary active transport (no ATP molecule is directly used), I'm just wondering if the whole mechanism is somehow "relying" on some concentration gradient created by some other pump: in this case, it'd be a secondary active transport.

Actually, Chloride ion (Cl-) should be WAY more concentrated in plasma. So it probably does not need anything to "boost" its plasmatic concentration and it should be "passive", as you said.

But again, I'm just assuming things 😛 I'd like some reliable sources.

 

[Kulsoom]

@greenmatter The point is cl shift only occurs when Conc of bicarbonate increases inside cells(which is normally less inside than outside) and cl is more outside cells than inside(normally).
so when HcO3 conc increases,it goes outside in exchange of cl which comes inside both via conc gradient.so i think its a passive transport.