Excretion of cesium and rubidium via the branchial potassium-transporting pathway in Mozambique tilapia

Abstract

Using an insolubilization technique in combination with element analysis, we examined the possible excretion of Cs+ and Rb+, both known to be biochemical analogs of K+, through the K+-transporting pathway in the gills of seawater-adapted Mozambique tilapia. To detect ion excretion from gills infused with Rb+ or Cs+, the isolated gills were treated with sodium tetraphenylborate, which reacts not only with K+ but also with Rb+ and Cs+ to form insoluble precipitates. The precipitates were formed specifically at the apical openings of mitochondrion-rich (MR) cells, which are responsible for K+ excretion in marine teleosts. Elemental analysis showed that Cs and Rb were distributed at the area of precipitates on the gill surface, and that these elements were colocalized with K. Our findings indicate that the gills eliminate unnecessary Cs+ and Rb+ in the body fluid, presumably through the same pathway as the K+ excretion in MR cells.