THE ROLE OF MUCUS IN ION ABSORPTION BY THE ESOPHAGUS OF THE SEA-WATER EEL (ANGUILLA-ANGUILLA L) - ELECTROPHYSIOLOGICAL, STRUCTURAL AND CYTOCHEMICAL INVESTIGATIONS

1. The structure of mucus in the oesophagus of the sea-water adapted eel, consists of a framework of fibers decreasing in density and thickness from the anterior to the posterior oesophagus. 2. With seawater in the lumen the mucus layer supports in vitro, about 45% of the lumen to serosa gradient of sodium ion activity along the whole oesophagus. It supports different chloride ion activity gradients: about 80% in the anterior and about 45% in the middle and posterior oesophagus. These results are confirmed by X-ray micro analysis. 3. Experiments without lumen-to-serosa gradients demonstrate a linked sodium and chloride active absorption appearing in the middle oesophagus and increasing towards the posterior oesophagus. 4. Na+ -K+-ATPase is cytochemically demonstrated but could not be inhibited by ouabain during in vitro experiments, due to its particular localization.