Fig. 2. The distribution of Na⁺,K⁺,2Cl^- cotransporter in SW-adapted and FW-acclimated killifish opercular epithelium. Images are confocal laser scans of NKCC revealed by immunofluorescence of mouse anti-human NKCC and goat anti-mouse IgG Oregon Green 488 in MR cells counterstained for mitochondria with Mitotracker Red (green fluorescence with red counterstain yields yellow). (A) In SW-adapted killifish, NKCC immunofluorescence at 7.5 µm from the surface of the chloride cells is evenly distributed throughout the cytoplasm of MR cells (white arrows). (B) In FW-acclimated killifish, NKCC immunofluorescence at 9.0 µm from the surface of the chloride cells is eccentrically distributed in the chloride cells and localized between pairs of MR cells (white arrows). Scale bar, 20 µm.