The free zinc concentration is quantified as "pZn," which, like pH, is the negative log10 of the molar concentration. 18 meg-ohm water from a DI source in the lab typically has 10-50 nm of Zn2+ (pZn 10 to 7.3). Is that a "healthy pZn for live cells or tissue ?
According to Documenta Geigy Sceintific Tables plasma or serum zince is 1.09 +/- 0.2 mg/L in adult humans (16.7 mM). About 35% of the serum zinc is bound to proteins. Common media such as RPMI1640 and Minimal eagles Medium do not contain zinc and I suppose this is provided by the serum suppplement. Thus 10-50 nM is not a healthy concentration in the absence of serum.
Interesting analysis. DOes anyone else have an idea on this ?
http://www.sigmaaldrich.com/life-science/cell-culture/learning-center/media-expert/zinc.html
I hope this is of some help.
Actually, I put this question up as a bit of a "poll" to see how many know or care anything about Zn2+ in biological solutions and media. The Sigma site is right about the physiological level of Zn2+, which is in the 100 pM to 1 nM range. Unfortunately, they do not know (or at least do not teach) the difference between total zinc in media (which is essentially irrelevant to cells) and the free zinc (Zn2+) which is critical. Anything over 10 NM and all of the zinc receptors in your cells and tissue are saturated. Anything over 100 NM and every cell in your dish starts to die within hours. Over 1 uM, and even the vertebrate fish die within hours. By the way, the solubility of Zn2+ at pH 7.4 is about 20 uM; anything over that will precipitate in minutes-to-hours. Fortunately, the albumin in serum will automatically buffer your Zn2+ to ~ 1 NM, so you are "automatically" in the right range so long as you do not exceed the albumin buffering capacity of your medium. However, with synthetic media you are on your own.
So then. When you read in a paper that someone added "10 uM" (or more) of zinc to a culture medium, you can be sure that he or she had no idea what he or she was doing. The effects of such grossly non-physiological treatments, moreover, are essentially meaningless. Compare this with a paper in which someone claimed that he had added " 20 uM of H+ ion to the bath....." but not told you what was the effect of that H+ upon the pH.
A good point, but bear in mind that serum albumin is 600 uM in blood plasma and since total zinc is 10 uM, there is a buffering capacity effect here. This will depend on the percent serum in a cell culture, but at a typical 10-20% the albumin concentration will be 60-120 uM, so adding 10 uM zinc will have a much smaller effect on pZn. You could do the math if you want to based on the following review:
http://www.biochemsoctrans.org/bst/036/1317/bst0361317.htm
If uptake is via endocytosis, then uptake may be different via the phagolysosome?
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