Excretion of cesium through potassium transport pathway in the gills of a marine teleost

Abstract

We used a newly developed technique that insolubilizes and visualizes K+ excreted from the gills to demonstrate that gill mitochondria-rich (MR) cells are responsible for K+ excretion in seawater-Acclimated Mozambique tilapia. To achieve a better understanding of the molecular mechanism of K+ excretion from the gills, we identified the cDNA sequences of some candidate molecules that may be involved in K+ transport. Of these candidate molecules, only a renal outer medullary K+ channel (ROMK) exhibited markedly upregulated mRNA levels in response to a high external K+ concentration. We found that ROMK expressed in the apical opening of MR cells was the main molecular pathway responsible for K+ excretion. Using the insolubilization technique, we further demonstrated the excretion of Cs+ and Rb+, which are known to be biochemical analogs of K+, through the K+ transport pathway in the gills of seawater tilapia. The activation of ROMK in the gill MR cells induced by K+ supplementation could eliminate unnecessary biochemical analogs of K+ more rapidly, possibly serving as an effective countermeasure against radiocesium in aquaculture.