Fig. 6. Effects of D1-like dopamine (DA) receptor agonists and antagonists on transepithelial potential differences (V_te) of posterior gills of Chasmagnathus granulatus. (A) 10 µmol l^-1 DA applied after pretreatment with the D1 antagonist, SCH23390 (10 µmol l^-1) produced the typical stimulatory phase, increasing V_te (^*P<0.05; N=5), but not the subsequent inhibitory phase observed in control conditions. (B) Addition of the D1 agonist fenoldopam (15 µmol l^-1) to posterior gills previously stimulated with the adenylyl cyclase activator forskolin (Forsk; 10 µmol l^-1) produced a partial reversion of the forskolin-induced increase of V_te (^*P<0.05; N=6; mean was obtained 100-120 min after the beginning of the experiment). Dotted line represents mean control value obtained after 20 min of perfusion with 30 saline.