Fig. 1. Specific activity of carbonic anhydrase (CA) ± SE measured in gill homogenates of Chasmagnathus granulatus acclimated to different salinities (10‰, 30‰, and 45‰, N = 6).

Fig. 2. Specific activity of carbonic anhydrase (CA) ± SE in microsomal and cytosolic fractions of anterior and posterior gills of Chasmagnathus granulatus acclimated to 10‰ and 30‰ (* represents comparisons with p < 0.001 between both fractions in anterior gills; a–b represents comparisons with p < 0.001 in posterior gills, N = 4).

Fig. 3. Differential induction of carbonic anhydrase activity (CA) in posterior gill homogenates of Chasmagnathus granulatus acclimated to diluted salinities (2‰ and 10‰) and seawater (30‰) (letters denote statistical differences with p < 0.05, N = 8).

Fig. 4. Specific activity of carbonic anhydrase (CA) ± SE in posterior gills of Chasmagnathus granulatus acclimated to 2‰ (hatched bars) or 10‰ (empty bars), perfused with 0.2 mmol L^− 1 acetazolamide (+ Az) (a–b, comparison with p < 0.01 between control and Az treatment in each salinity, N = 5–7).

Fig. 5. Transepithelial potential difference (V_te) in isolated perfused posterior gills of Chasmagnathus granulatus acclimated to 2‰ salinity. 5 mmol L^− 1 ouabain (Ou, inhibitor of Na⁺/K⁺–ATPase) and 0.2 mmol L^− 1 acetazolamide (Az, inhibitor of CA) were applied basolaterally (N = 5–6). (A) Az applied before Ou. (B) Ou applied before Az, drugs were applied during symmetrical perfusion first with 20‰ and second with 30‰ saline solution (Ctrl = Control).

Fig. 6. Transepithelial potential difference (V_te) in isolated perfused posterior gills of Chasmagnathus granulatus acclimated to 2‰. Symmetrical perfusion was carried out with saline 20‰. Dimethylsulphoxide (0.1% DMSO) in the bath produced a non-significant effect. Addition of 1 μmol l^− 1 bafilomycin A₁ (inhibitor of V–H⁺–ATPase) in DMSO to the bath solution significantly reduced the V_te (a–b, comparison with p < 0.01, N = 9).

Fig. 7. Transepithelial potential difference (V_te) in isolated perfused posterior gills of Chasmagnathus granulatus acclimated to 2‰. (A) 2 mmol L^− 1 SITS (inhibitor of Cl⁻/HCO₃⁻ exchanger) was applied in the bath solution (a–b, comparison with p < 0.05, N = 7). (B) 5 mmol L^− 1 Ouabain (Ou, inhibitor of Na⁺/K⁺–ATPase) was applied basolaterally and further combined with 2 mmol L^− 1 SITS (*, comparison with p < 0.01 between treatments and control, N = 5).

Fig. 8. Transepithelial potential difference (V_te) in isolated posterior gills of Chasmagnathus granulatus acclimated to 2‰, symmetrically perfused with 20‰ Na-free saline. (A) Basolateral addition of 1 μmol l^− 1 bafilomycin A₁ in 0.1% DMSO (a–b, comparison with p < 0.05, N = 4). (B) 2 mmol L^− 1 SITS, dissolved in the bath solution (a–b, comparison with p < 0.05, N = 5).

Composition of the saline solutions used in the perfusion experiments, expressed as mmol L^− 1

Glucose (2 mmol L^− 1) was added only to the perfusates.