Expression analysis of Mg2+ transporters in the kidney of marine and euryhaline puffer fishes

Abstract

In marine fish, Mg2+ concentration in bladder urine and plasma are maintained approximately 150 mM and 2 mM respectively. An important function of the marine teleost kidney is elimination of excess divalent ions (magnesium and sulfate) which is abundant in ingested sea water. The SO42− transporter involved has recently been identified but the one involved in Mg2+excretion remains to be identified. River puffer (mefugu, Takifugu obscurus) is an ideal fish species for such studies since it is a euryhaline species and the complete genome sequence of a close relative tiger puffer (torafugu, Takifugu rubripes), a marine fish, is available. In this study, we have identified candidate Mg2+ transporters of the Slc8, Slc24, Slc41 and TRPM families by database mining and analyzed their tissue expression patterns. Among the candidates, we selected transporters whose expression was highly induced in the kidneys of river puffers after transfer from fresh water to seawater. We are now performing immunohistochemistry and functional characterization of the candidates to demonstrate that they are the long-sought Mg2+ transporters responsible for the renal elimination of excess Mg2+contained in seawater ingested by marine teleosts. This work is supported by “Global Centers of Excellence Program of Japan Ministry of Education, Culture, Sports, Science, and Technology (MEXT).