Fig. 4. Immunocytochemical staining of vacuolar ATPase B subunit isoforms vatB1 and vatB2 in swimbladder gas gland cells from Anguilla anguilla. Both antibodies revealed positive staining only in gas gland epithelial cells. (A) Antibody #1034 (rabbit anti-vatB1+vatB2) revealed a positive staining of apical and basolateral membranes. A very intense signal was also observed in apical vesicles. (B) Staining with antibody #1035, which is specific for the vatB1 isoform (kidney isoform), resulted in a similar picture in the apical region of the cells, but in the basolateral region very little staining was observed. No background staining was observed in the negative control (C). Scale bars, 10 µm. Arrows point to positive staining reaction in basolateral membranes.