Saltwater fish drink large amounts of seawater every day, and the boric acid contained in seawater is toxic when it accumulates in the body.Therefore, it is thought that saltwater fish have some mechanism to excrete boric acid, but it has remained a mystery until now.

 A group including the Tokyo Institute of Technology, Mayo Medical School (USA), the University of Tokyo, and Kaiyukan Co., Ltd. investigated boric acid in the bodies of seawater-raised and freshwater-raised pufferfish.First, the intestinal boric acid concentration of puffer fish raised in seawater containing 450 μM boric acid was 150 μM.Since the concentration of boric acid in the intestinal fluid was significantly lower than that in seawater, it was thought that marine puffer fish absorbed boric acid in the intestine.

 Next, when the urinary boric acid concentration was compared, it was 19,000 μM in the seawater-raised blowfish and 20 μM in the freshwater-raised blowfish.The urine of saltwater-raised pufferfish contained 1,000 times more boric acid than that of freshwater-raised pufferfish, suggesting that marine pufferfish concentrate and excrete boric acid absorbed from the intestine into the urine. was done.

 Therefore, in order to elucidate the boric acid excretion mechanism, the research group conducted comprehensive gene expression analysis in the pufferfish kidney, and found that the membrane transporter "Solute carrier family 4 member 11A (Slc4a11A)" whose expression level increases during seawater feeding. )” was found.We investigated the activity of Slc4a11A by electrophysiological techniques and confirmed that it is an electrogenic transporter that responds to boric acid. Slc4a11A is said to be able to transport boric acid into the urine against the concentration gradient, driven by the pH gradient and potential difference between the intracellular and extracellular regions, and can produce urine containing high levels of boric acid.

 From the above, we clarified the internal mechanism and pathway of urinary borate excretion in marine fish, and showed that Slc4a11A plays an important role among them.The results of this research are expected to contribute to the elucidation of the seawater adaptation mechanism of marine organisms and to be applied to sustainable saltwater fish farming.

Paper information:[The Journal of Biological Chemistry] Seawater fish use an electrogenic boric acid transporter, Slc4a11A, for boricacid excretion by the kidney

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