MCCORMICK, Stephen D.; HIROI, Junya; USGS, Conte Anadromous Fish Research Center, Turners Falls, MA, USA: The effect of salinity on CFTR, NKCC, and Na,K-ATPase in gill chloride cells of teleost fish.

The localization, quantitation and effect of salinity on the cystic fibrosis transmembrane regulator (CFTR), Na,K,2Cl cotransporter (NKCC) and sodium pump (Na,K-ATPase) were examined in the gills of several species of teleost fish. High levels of NKCC and Na,K-ATPase were found only in chloride cells, also known as mitochondrion-rich cells. In all species NKCC and Na,K-ATPase had an extensive basolateral distribution in chloride cells in seawater. In most species both transporters also had a basolateral distribution in fresh water, but tilapia had an apical distribution of NKCC in chloride cells in fresh water, perhaps indicative of an absorptive isoform. CFTR was barely detectable or absent in chloride cells in fresh water, and was strongly upregulated after seawater exposure with an exclusively apical distribution. CFTR immunolocalization will therefore be a useful method for identifying functional salt secretory cells in teleost fish. By localizing all three transporters to chloride cells, the present findings provide support for the current model of salt secretion in teleosts indicating all three transporters are involved in salt secretion. Our results also indicate there is species-specific regulation of these transporters in response to salinity.