My understanding of Naviaux's cell danger response hypothesis is that elevated levels of extracellular ATP (which is coming out of damaged/dying cells) is what signals danger to neighbouring cells via its actions on the purinergic receptors.
Indeed. I think cell death might be the most well established source of ATP danger signalling, but also (from Naviaux's 2014 "
Metabolic features of the cell danger response", with my emphasis):
4.3. ATP
Purinergic signaling nucleotides like ATP, ADP, UTP, and UDP are released in increased amounts from cells under stress and activate inflammation (Xia et al., 2012). Cells need not be broken or lysed to increase the release of ATP, other nucleotides, and metabolites. ATP and sodium urate crystals are activators of NLRP3 inflammasome assembly (Riteauet al., 2012). Purinergic signaling via ATP directly stimulates cortisol synthesis and release from the adrenal cortex, independent of ACTH stimulation (Kawamura et al., 1991).
So directly released for danger singaling, from live (but stressed) cells. And also as an ubiquitous neurotransmitter:
Skepticism was high in the early days that extracellular ATP could actually be a neurotransmitter. With the cloning of 19 different purinergic receptors that are widely distributed in every neural and non-neural tissue of the body, this early skepticism has been soundly extinguished [...]. Today, the role of purinergic signaling continues to expand virtually into every fundamental cell communication, stress response, autonomic, vestibular, and sensory integration pathway known [...].
(Could it be possible to exhaust ATP too fast via (excessive) neurotransmission? Wired leads directly to tired?)
See also
Wikipedia on ATP extracellular signalling. Also from there: your entire body (should) contain about 100g of ATP in total, with each molecule recycled about 500 to 750 times each day, you should burn through your entire body weight in ATP daily! (Wow.)
Even though ATP levels fluctuate, total ATP + ADP should stay as roughly constant. So I wonder what the new study has to say about ADP levels? (Not a single mention of "ADP" in there.) If our ATP is supposed to be raised, is the total pool still the same, higher or lower?
The Myhill paper talks about reduced ADP transfer into the mitrocondria via the ADP-ATP translocator protein (on the mitochondrial impermeable inner membrane), which they say is being blocked (in some cases). They lament that:
In many studies of mitochondrial function, mainly concerning the individual complexes I-V of the ETC, the role of the ADP-ATP translocator protein TL is largely ignored.
Which does kind of sound like what this new study did (including looking at, and finding no, differences in the electron transport chain complexes I-IV activity). And they say they've responded to other (similar) studies that used blood mononuclear cells (PBMCs), as this one did. (But I don't know where their comment to
this one, linked as an example, can be found...?)
In the new study they used "
oligomycin to block mitochondrial ATP synthesis, and thus the remaining ATP content represented that from non-mitochondrial reactions such as glycolysis". But the Myhill study went a step further, using "
sodium azide to inhibit ATP production prior to a two-stage re-measurement of ATP" - first with mitochondria having been inhibited for 3 minutes (that's how quickly an entire cell's ATP store is totally depleted). And then again after washing away the azide inhibitor, to see how fast ATP replenished (I couldn't grasp the results of this, possibly due to getting lost in their nomenclature).
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3403556/figure/fig03/
Above histogram shows that healthy controls had their ATP synthesis cut down to an average of 7.5% of total when the electron transport chain (ETC, in mitochondria) was blocked. Roughly as expected, since the ETC produces an extra 30 ATP molecules for the 2 that come from glycolosis, alone, of a single glucose molecule - i.e. 1/16th efficiency (or 6.3%). While ATP synthesis of those in the B sub-group of CFS-ME patients, in green, was
massively less effected by blocking the efficient ETC pathway.
It's quite startling how much more efficient the mitochondrial ETC makes cellular energy creation. 16 times more than glycolosis alone. A very potent 'afterburner'... So I guess, with either paper, whether enhanced glycolosis (or some other route?) is just compensatory, or if it is in fact stealing the show in being over-active, somehow, either ways, it's going to make for a whole lot less useful energy output per calorie in! (Even with just a relatively small deviation.)
Sorry, more waffling...