Active Cl− absorption by the Chinese crab (Eriocheir sinensis) gill epithelium measured by transepithelial potential difference

Isolated posterior gills from Chinese crabs (Eriocheir sinensis) acclimated to tap-water were perfused and bathed with full, physiological saline (containing Na+ and Cl−). Under these conditions they developed an outside positive transepithelial potential difference (PDte). Substitution of Na+ by choline on both sides of the epithelium resulted in a substantial hyperpolarization of the PDte, while substitution of Cl− by gluconate reverses PDte to outside negative values.