Influence of salinity on the localization of Na+/K+-ATPase, Na+/K+/2Cl-cotransporter (NKCC) and CFTR anion channel in chloride cells of the Hawaiian goby (Stenogobius hawaiiensis)

Na+/K+-ATPase, Na+/K+/2Cl(-) cotransporter (NKCC) and cystic fibrosis transmembrane conductance regulator (CFTR) are the three major transport proteins thought to be involved in chloride secretion in teleost fish. If-this is the case, the levels of these transporters should be high in chloride cells of seawater-acclimated fish. We therefore examined the influence of salinity on immunolocalization of Na+/K+-ATPase, NKCC and CFTR in the gills of the Hawaiian goby (Stenogobius hawaiiensis). Fish were acclimated to freshwater and 20parts per thousand and 30parts per thousand seawater for 10 days. Na+/K+-ATPase and NKCC were localized specificatly to chloride cells and stained throughout most of the cell except for the nucleus and the most apical region, indicating a bisolateral/tubular distribution. All Na+/K+-ATPase-positive chloride cells were also positive for NKCC in all salinities. Salinity caused a slight increase in chloride cell number and size and a slight decrease in staining intensity for Na+/K+-ATPase and NKCC, but the basic pattern of localization was not altered. Gill Na+/K+-ATPase activity was also not affected by salinity. CFTR was localized to the apical surface of chloride cells, and only cells staining positive for Na+/K+-ATPase were CFTR-positive. CFTR-positive cells greatly increased in number (5-fold), area stained (53%) and intensity (29%) after, seawater acclimation. In freshwater, CFTR immunoreactivity was light and occurred over a broad apical surface on chloride cells, whereas in seawater there was intense immunoreactivity around the apical pit (which was. often punctate in appearance) and a light subapical staining. The results indicate that Na+/K+-ATPase, NKCC and CYTR are all present in chloride cells and support current models that all three are responsible for chloride secretion by chloride cells of teleost fish.