Fig. 3. (A) Identification of PNA⁺ and PNA^– negative mitochondria-rich cells (MRCs) in gill sections from adult rainbow trout. PNA⁺ MRCs are labelled with arrows; stars indicate PNA^– MRCs. MRCs were identified on the basis of immunoreactivity against Na⁺/K⁺-ATPase (red); green indicates apical PNA and blue indicates nuclei (DAPI). (B) Higher magnification image of a PNA (green)-positive MRC. Negative controls included (C) omission of primary antibody against Na⁺/K⁺-ATPase and of biotinylated PNA. The image in C was captured using the same exposure and microscope settings as in A. Scale bar in A, 20 µm; and in B, 5 µm.