Effects of ouabain on chloride movements across the seawater eel intestine

Summary

Simultaneous measurements of transepithelial potential difference (PD) and net water flux were made in the stripped intestine of seawater eels, and the effects of ouabain on these two parameters were examined in normal Ringer solution or under a chloride concentration gradient. Ouabain reduced the serosa-negative PD and the net water flux in normal Ringer solution with a linear relationship between the PD and the net water flux. Removal of K⁺ from the Ringer solution on both serosal and mucosal sides also reduced the PD and the net water flux to approximately zero. On the other hand, blocking the Na⁺−K⁺ pump by ouabain, K⁺-free or Na⁺-free Ringer solution increased the diffusion potential for Cl⁻. Inhibition of Cl⁻ transport and increment in Cl⁻ permeability by ouabain occurred almost simultaneously. It is likely, therefore, that Cl⁻ transport as well as Cl⁻ permeability is dependent on Na⁺−K⁺ pump activity. A possible mechanism of dependence of Cl⁻ transport on the Na⁺−K⁺ pump is discussed in relation to the increment in Cl⁻ permeability.