Lactate the cause of exercise induced acidosis?

K

Karky

2
So the traditional belief that lactic acid causes exercise induced acidosis by releasing a hydrogen has been challenged a lot lately. Are anyone in the know on this debate? I haven't really been following it.

When you have no oxygen, pyruvate (C3H4O3) takes on 2 hydrogens (from NADH and H+ formed in glycolysis) an forms lactic acid (C3H6O3) this quickly forms LA- (C3H5O3-) and a hydrogen ion (H+)

If pyruvate didn't do this, then NADH wouldn't be "recycled" to NAD+ and glycolysis would come to a halt because there would be no NAD+ left.

But of course, this leaves us with hydrogen ions, which will cause acidosis when they accumulate to the point where the buffering system can't buffer them quickly enough. When the environment gets acidic, enzyme function becomes reduced and fatigue sets in.

Now of course, if it wasn't for pyruvate being able to form lactic acid, we would have to stop moving a lot sooner, so it really is a good thing.

Did that pretty much sum up the traditional stance? Or did I misunderstand something? If the traditional stance is wrong, then how is it really?
 
I always thought that lactate was a consequence rather than a cause of the biochemistry that cause acidosis. In fact, I actually thought lactate would reduce acidosis.

I can't remember my organic chemistry very well ... I need more info, Karky :)

I think this is a very interesting topic for discussion.
 
Yes, it should reduce it, as it acts as a buffer, taking on The H from NADH and the free H+ that is expelled I think in the 6th reaction of glycolysis. But after that, one H+ is dissociated from it.. and like I said, if this didn't happen, NADH wouldn't be "recycled" to NAD+ (oxidative phosphorylization recycles NADH to NAD+ under aerobic conditions, but under anaerobic conditions pyruvate has to do it by forming lactic acid) and the 6th reaction of glycolysis would come stop, thus stopping the entire thing. But then there would be no build up of H+ at all, but you wouldn't be able to keep exercising as there would be no more ATP production.

That's the way I've understood it..

but then others have said that lactic acid can't be created from glycolysis or something like that, as there is not enough H+ involved there to do so.. Also, of course, when ATP creates ADP and energy, a H+ is released. Puruvate would probably buffer this and create lactate.. but I'm not sure. I'd love if someone who knows a lot about this could chime in. Because I'm kinda confused.
 
Also, I've heard once lactate acid is formed (if it is formed) it pretty much immediately converts to lactate + H+.. and if that is the case, and you won't be able to get it out of the muscle before that happens, what's the point in doing different things to remove lactate from the muscles.. I mean, lactate in itself is harmless, it doesn't release any protons (it already has, so to speak).. I'm confused :(
 
OK, I understand what you're saying now. But I don't know the answer. I can try to find out, but I think we need a biochemist to answer this one :)
 
Simply because A happens and then B happens doesn't mean A caused B, or B caused A. In this case we're talking about acidosis and lactic acid (or sodium lactate). Concentration of sodium lactate is rather a marker for the metabolic conditions of the cell and not a cause. The change in pH (acidosis) is rather due to the general rxns of glycolysis and ATP hydrolysis. Lactate production actually takes up hydrogen ions, and assists in alkylating the cellular matrix.

I've got a sweet study on this saved somewhere, I'll look for it. But just so you know, the lactate = acidosis theory has been debunked a while ago.
 
that was kind of a good read. I didn't really understand all of it, but maybe tomorrow I can sit down and really go through it. It goes through the different reactions that happen and explain in what reactions protons are "expelled" and in what reactions they are "consumed" and how an imbalance occurs.

But basically, every time you use ATP for something, a proton results, which will build up and cause acidosis if your body can't buffer them. And when you're out of oxygen, your body won't be able to buffer them anymore. And of course, with protons comes lactate, since lactate is formed when pyruvate buffers a proton, so the more protons you have the more lactate you have, and thus looking at lactate levels can say something about how acidic the environment is. Does that sum it up decently?
 
mreik said:
Simply because A happens and then B happens doesn't mean A caused B, or B caused A. In this case we're talking about acidosis and lactic acid (or sodium lactate). Concentration of sodium lactate is rather a marker for the metabolic conditions of the cell and not a cause. The change in pH (acidosis) is rather due to the general rxns of glycolysis and ATP hydrolysis. Lactate production actually takes up hydrogen ions, and assists in alkylating the cellular matrix.

I've got a sweet study on this saved somewhere, I'll look for it. But just so you know, the lactate = acidosis theory has been debunked a while ago.
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Isn't that the same as what I said?
 
not really, the lactate is not a consequence of the acidosis, nor the other way around, both are in fact exclusive consequences of the cell functioning properly to produce energy
 
mreik said:
Lol.. yup. I read through the thread, and then went on a search for the article, couldn't find it and just answered his Qs again :boxing_smiley: :D
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No problem ... I'm just easily confused, and I thought maybe I just didn't understand the question or the answer :D
 
limestix said:
not really, the lactate is not a consequence of the acidosis, nor the other way around, both are in fact exclusive consequences of the cell functioning properly to produce energy
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But isn't lactate a consequence of protons accumulating?
 
Had a PM exchange with Mreik:
The parts in bold are his answers

mreik said:
Karky said:
So, the burn you feel during exercise, what does that come from? Are we just feeling the acidosis in the muscle, and not really the lactate, like we say we do?
Right, it comes from the muscle being overwhelmed with hydrogen ions (H+), and not enough bicarb or anything to buffer it.
Also, since lactate isn't really bad, why is it so important to get rid of by for example taking a brist walk when you're done with anaerobic training.
This is one of those things that will clear ANYTHING out of the muscle, and yes lactate too. So this still works, just not the way most people think it does. Improving blood flow will flush the lactate out (and help it get to the liver to be made into glucose/pyruvate), it will flush out the H+, and bring in some bicarbonate to help buffer the cellular environment.
Is this just to get the lactate quicker to the liver so it can be turned into glucose. Or does the increased blood flow also contribute to a faster reduction of acidosis? I'd think that the more blood flow there was to a muscle in acidosis, the more buffering agents would come in a shorter amount of time, resulting in you getting out of acidosis faster. Would this be correct?
Yeah, damn I shoulda kept reading before I typed that lol
Also, I read about how acids have a functional group that releases the proton.. but that when pyruvate is formed, there is no proton in this group.. so pyruvate actually has 3H (not 4)Yeah this is the lactate we speak of, lactic acid has the H still attached. Easily referred to as the unprotonated and protonated respectively., and there is no H in the functional group, and when lactate is produced and 2H joins, these are not joined to the functional group, thus lactate can't expell a proton and contribute to acidosis.
Word.
I read about it here:
under "glycolysis" (it explains how pyruvate has no H in it's functional carboxyl group)
under "The Lactate Dehydrogenase Reaction" it explains how the Hs added don't add to this group..


I'm not gonna pretend to understand all of it (that's why I'm asking you to tell me whether I understand it or not :p), you might also need to read more from the article to get the context, I'd appritiate it if you'd take the time to help me, but I'd understand it if you've got other things to do :p I'm just trying to understand exactly why it's wrong to blame lactate for acidosis :p
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Click to expand...
 
A quick look at a bio text could easily solve the problem.

Fact is, when a cell is producing energy aerobically, it does not produce it at such a rate that H+ builds up; that is to say that, the H+ is used as it comes. NAD+ is recycled productively and glycolysis continues smoothly.

However, once you enter anaerobic glycolysis, the body begins producing additional ATP through fermentation. since it is going faster, NAD+ is not being produced fast enough, so it uses pyruvate to take an H+ iron from NADH to form NAD+ and lactate. The NAD+ can then be used to continue the process of glycolysis.

The acidosis is simply caused by the increase in speed of ATP production. The lactate production is necessary in order to keep NAD+ in steady supply, because without it glycolysis would stop and the cell would run out of energy.
The lactate actually helps reduce acidosis by taking an H+ from NADH rather than having the H+ move across the membrane and continue oxidative phosphorylation. (the anaerobic environment means oxygen is in low supply so oxidative phosphorylation can only go so fast, which is why there is a build up of H+ causing acidosis)

Well thats about the best I can make of it. I could be wrong. Sorry if i explained it poorly haha. I don't completely understand it myself.

I guess a simpler(ish) version is:

In an anaerobic environment, there isnt enough oxygen to continue oxidative phosphorylation as fast as H+ is being produced. Therefore acidosis occurs. Lactate is produced in a different process that is used to free up NAD+ to continue glycolysis, and an indirect effect of this process is a reduction of acidosis.

I guess if the lactate didnt take the H+, it would be put back in the electron transport chain and into oxy phos process that is already being overloaded due to lack of oxygen.

Please pelase someone with a better understanding straighten this out, I'm getting more confused as I go on
 
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Also I believe pyruvate would be the strongest base floating around, so that's why it sucks up excess H+ and becomes lactate (your body wants to always maintain a homeostatic pH).

But then again, maybe my organic chemistry is failing me ... I think I'm tired and my brain is hungry :)

I need to eat.
 
Danke, Mreik ;)
 
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