Sodium-glucose interactions in the goldfish intestine.

1. Everted sacs of goldfish intestine transfer glucose and water to their serosal surfaces and the total transfer is greater in the anterior intestine than in the intestinal bulb or rectum.2. Transmural potentials, with the serosa positive to the mucosa, were recorded from all parts of the goldfish intestine but were highest in the anterior intestine and the rectum. In both these areas the total potential was dependent partly upon the presence of glucose.3. Reducing the concentration of sodium bathing the mucosa of the anterior intestine reduced the glucose-evoked potential in a non-linear way. The steady-state potentials, with or without glucose, first increased and later decreased as the sodium concentration was further reduced.4. Reducing the concentration of glucose bathing the mucosa from 27 to 5 mM slightly increased the glucose-evoked potential. Further reduction of the glucose concentration caused the glucose-evoked potential to fall.5. Phlorrhizin inhibited the glucose-evoked potential. The degree of inhibition was proportional to the log concentration of phlorrhizin over the range 2 x 10(-7)-6 x 10(-5)M. The steady-state potential with glucose present was lower than when glucose was absent at phlorrhizin concentrations, 6 x 10(-6)-6 x 10(-5)M.6. The glucose-evoked potential increased rapidly over the temperature range 5-15 degrees C and more slowly from 15 to 30 degrees C. The steady-state potentials also increased with temperature, the rate of increase being greater when glucose was present. Below 15 degrees C the glucose-independent potential was higher and above 15 degrees C lower than the steady-state potential recorded with glucose present.7. These findings are discussed in terms of sodium-glucose interaction taking place at the luminal side of the mucosal cell, on the outside of the mucosal cell membrane.