Fig. 7. Immuno-electron micrographs of the vacuolar-type proton pump (V-ATPase) in gill chloride cells of killifish adapted to low-NaCl (A,B) and mid-NaCl (C,D). V-ATPase immunoreactivity was detected in the tubular system (arrows) continuous with the basolateral membrane, but not in the apical membrane (asterisks) and mitochondria (m) in mitochondria-rich (MR) cells (A,C). (B,D) Magnified views of the cytoplasm in MR cells. The staining was more intense in the low-NaCl environment than in the mid-NaCl environment. pv, pavement cell. Scale bars, 1 µm (A,C); 0.5 µm (B,D).