Chloride-dependent sodium and water transport in the seawater eel intestine

Abstract

Simultaneous measurements of transepithelial potential difference (PD) and net water flux were made in the stripped seawater eel intestine, and the effects of removal of Ca2+ and replacement of Cl− with other anions on these two parameters were examined. Removal of Ca2+ from normal (NaCl) Ringer solution on both mucosal and serosal sides reduced the serosa-negative PD and the net water flux. Since SO 4 2− binds Ca2+ strongly, the effects of substitution of SO 4 2− for Cl− could be due to deficiency in both Cl− and Ca2+. Among five anions used in this study, CH3SO 4 − (with low affinity to Ca2+) seems to be the most suitable substitute for Cl−. When both mucosal and serosal Cl− were replaced with CH3SO 4 − , both the PD and the net water flux decreased to approximately zero. When mucosal Cl− was replaced progressively with other anions, the serosa-negative PD and the net water flux decreased in association with the decrease in Cl− concentration, and a linear regression was observed between the decrease in the net water flux and that in the PD. These results indicate that Na+ and water transport depend closely on Cl− transport.