Protein-Bound vs. Free (Ionized) Calcium

[asaha]

Hello,

I understand that plasma calcium is found in both protein-bound and free (ionized) forms. Why does alkalosis increase the amount that is protein-bound?

Thanks in advance!

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[UCLAstudent]

Calcium and H+ compete for some of the same protein binding spots. With a drop in H+ (alkalosis), this frees up some of the protein binding spots for calcium and leads to lower levels of free calcium.

 

[goodies]

patient hyperventilates and blows of Co2 --> respiratory alkalosis --> increased pH --> increased negative charges on albumin, increased binding of calcium to albumin without decrease in total ca++; decreased ionized calcium --> tetany

it is due to a competition of sodium and calcium for channels in neurons. i don't think its with hydrogen

 

[blz]

UCLAstudent is right. Ca++ binds apartic and glutamic acid residues on albumin. these AAs are very sensitive to pH. A higher PH deprotonates them even more allowing greater binding of Ca.

 

[predodoc]

How many of you learned that from Goljan?

 

[doctorp82]

I learned it from Chvostek and Trousseau

I wonder how cool you had to be to have two sign's named after you (Trousseau)?

 

[blz]

learned the ca stuff from class.


speaking of signs, I think the Chandelier sign is the coolest. also, Courvoisier's sign just sounds badass.

 

[UCLAstudent]

I learned it from BRS Physio.

 

[goodies]

the info i got was from BSS (board simulator series)

 

[Idiopathic]

the info i got was from BSS (board simulator series)

AKA: Goljan

I learned it myself from the man, he has a great diagram.

 

[guitarguy09]

I just listened to that lecture actually and Goljan clearly states that as well, just as mentioned above. G-dog is the man.

 

[winsicle]

patient hyperventilates and blows of Co2 --> respiratory alkalosis --> increased pH --> increased negative charges on albumin, increased binding of calcium to albumin without decrease in total ca++; decreased ionized calcium --> tetany

it is due to a competition of sodium and calcium for channels in neurons. i don't think its with hydrogen

UCLAstudent was talking about the competition b/t H+ and Ca++ for binding sites on Albumin...

you were talking about the tetany mechanism on neurons:

which i think just has to do w/ the altered Membrane Potential (due to decreased extracellular/positively-charged 'free' Ca++)
--> less depolarization is needed to get to the threshold potential and so there is increased firing of AP --> muscle contraction

(i've never heard of the Na++/Ca++ competition for channels in neurons)

 

[SOUNDMAN]

In regards to neurons I believe hypocalcemia leads to tetany by obviously lowering the threshold of the neuron. This occurs d/t Na+ channels becoming more permeable to Na+, and thus more Na+ leaking into the neuron thus lowering the threshold. That's how I've understood it.

 

[winsicle]

In regards to neurons I believe hypocalcemia leads to tetany by obviously lowering the threshold of the neuron. This occurs d/t Na+ channels becoming more permeable to Na+, and thus more Na+ leaking into the neuron thus lowering the threshold. That's how I've understood it.

yeah the voltage gated Na++ channels become activated b/c of the lowered threshold, but there's no "competition" w/ Ca++