Ca2+ protect zebrafish embryos from water acidification.

Ionizable strategies are routinely used to enhance the solubility and dissolution rates of various pharmaceuticals. These chemicals may directly affect aquatic environment once discharged from factories, hospitals or livestock farms. Here, we assessed the potential side effect of tetracyclines (TCs) on the development of zebrafish embryos. Tetracycline hydrochloride decreased water pH from 6.4 to 4.4 at 30 mg/L. Acidified water exceeded the tolerance of zebrafish embryos in pure water during the early ten hours post fertilization (hpf). Interestingly, we found that Ca2+ in the embryo medium could increase the tolerance of embryos to acidified water. Furthermore, we found that the protection of Ca2+ was not due to the formation of TCs-Ca2+ complexes under acidic condition, based on spectral analysis. Meanwhile we showed that exogenous addition of Ca2+ could inhibit the accumulation of Ca2+ from the cytoplasm to the surface of embryos. These results may shed light on the strategies for protecting aquatic animals from acidic environments.