Abstract
Magnesium (Mg) is the second most common cation in seawater as well as the second most abundant intracellular cation. Its importance is relevant in cell proliferation and proper signaling, ensuring adequate muscle function, and is implicated in human diseases like cancer and ischemia if Mg-homeostasis is disrupted for extended periods. Coupled with sulfate, Mg has been found to impair water absorption within the intestinal lumen of marine teleosts and limit survivability of in hypersaline environments. This study utilized an experimental infusion of MgCl2, with a salt-load of 50 mmol/kg/h, delivered directly into the circulatory system of gulf toadfish (Opsanus beta) via a PE50 catheter, purposefully disrupting Mg homeostasis. A control group was delivered NaCl, with a similar chloride concentration to the experimental infusion, to ensure that detected physiological changes of this study were primarily due to Mg. Fluid and tissue samples were collected from control and experimental animals and later analyzed through Flame Atomic Absorption Spectrometry and molecular assessment. A significant difference was found in blood plasma concentrations between study groups after 24 and 72-hour intervals, elucidating that the infusion successfully disrupted Mg-homeostasis and allowed for downstream renal function to be assessed. There was also a significant difference found between study groups in the urine volume produced as well as the total bladder Mg2+ content of O. beta, following the salinity loading. Succeeding the influence of the infusion on study animals, qPCR analysis on transient receptor potential melastatin (TRPM) ion channels members 6 & 7 provided results revealing a general trend of upregulation compared to a housekeeping gene, b-actin, in both kidney and urinary bladder tissues. A significant difference was shown to exist between study groups expression of trpm7 of the urinary bladders in O. beta, describing a vital role that the understudied organ plays in osmoregulatory homeostasis, and suggesting a redirection of metabolic energy which could insinuate decreased survivability with prolonged exposure. Evident upregulation of Mg transporter proteins, as well as a specific, significant increase of trpm7 ion channels from an experimental infusion is useful for future studies in that it presents a physiological struggle saltwater fish experience when exposed to elevated Mg, a common issue faced in natural ecosystems.