title: Bicarbonate secreted from the pancreas contributed to the formation of Ca precipitates in Japanese eel, Anguilla japonica.
abstract: Marine teleosts produce Ca precipitates in the intestine as a product of osmoregulation. Ca precipitates are formed by a chemical reaction of Mg(2+) and Ca(2+) derived from ingested seawater with bicarbonate (HCO(3)(-)). It has been reported that HCO(3)(-) originates from the intestine; however, the pancreas is predicted to be another organ that may supply HCO(3)(-) to the intestinal tract. In the present study, the pancreas was surgically removed from Japanese eel to confirm its contribution to Ca precipitate formation. Pancreatectomized eel produced significantly less Ca precipitates than control eel in seawater, indicating that HCO(3)(-) from the pancreas contributes substantially to the formation of Ca precipitates. To further examine the molecular mechanisms of HCO(3)(-) secretion, we cloned cDNAs encoding HCO(3)(-) transporters and identified those transporters that elevated their mRNA expression in the intestine and pancreas following seawater transfer. In the intestine, mRNA expression of Slc26a6A was increased shortly after seawater transfer, whereas Slc26a1 mRNA expression increased gradually following seawater transfer. In the pancreas, Slc26a3 mRNA expression was high during the early stage of seawater acclimation, whereas Slc26a1 expression increased gradually after transfer to seawater. In the intestine and pancreas, therefore, both transient and progressively increasing types of HCO(3)(-) transporters are likely to be involved in HCO(3)(-) secretion into the intestinal lumen in a coordinated manner.
authors.affiliation: Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo, Tokyo, Japan. mekuchim@affrc.go.jp
authors.forename: Miyuki
authors.initials: M
authors.lastname: Mekuchi
authors.forename: Soichi
authors.initials: S
authors.lastname: Watanabe
authors.forename: Toyoji
authors.initials: T
authors.lastname: Kaneko
mesh_terms: D000064:Acclimatization / Q000502:physiology; D000811:Anguilla / Q000378:metabolism*; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D003001:Cloning, Molecular; D007413:Intestinal Mucosa / Q000378:metabolism*; D010179:Pancreas / Q000378:metabolism*; D012313:RNA / Q000737:chemistry / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction / Q000662:veterinary; D014882:Water-Electrolyte Balance
chemical_list: D001639:Bicarbonates; D012313:RNA; D002118:Calcium