Intestinal HCO secretion in Amphiuma: Stimulation by mucosal Cl and serosal Na

The requirement for Na and Cl in the bathing media to obtain a maximal HCO secretory flux ( {Mathematical expression}) across isolated short-circuited Amphiuma duodenum was investigated using titration techniques and ion substitution. Upon substitution of media Na with choline, HCO secretion was markedly reduced. Replacement of media Cl produced a smaller reduction of {Mathematical expression}. The presence of Cl enhanced HCO secretion only if Na was also in the media. Elevation of media Na or Cl in the presence of the other ion produced a saturable increase of {Mathematical expression}. In the presence of Na, Cl stimulated {Mathematical expression} when added to the mucosal but not the serosal medium. In the presence of Cl, Na elevated {Mathematical expression} when added to the serosal but not the mucosal medium. The ability of mucosal Cl to stimulate {Mathematical expression} was not apparently dependent on mucosal Na. Simultaneous addition of 10 mm Cl to the Na-free mucosal medium and 10 mm Na to the Cl-free serosal medium stimulated {Mathematical expression} above levels produced by serosal Na alone. In conclusion, intestinal HCO secretion required mucosal Cl and serosal Na and did not involve mucosal NaCl cotransport. The results are consistent with a mucosal Cl absorptive mechanism in series with parallel basolateral Na-H and Cl-HCO exchange mechanisms. © 1982 Springer-Verlag New York Inc.