Studies on transmural potentials in vitro in relation to intestinal absorption

The dependence on Na⁺ of the active transport of sugar in small intestine, in vitro, was studied by observing the influence of various sugars on the electrical potential difference measured across the wall of everted intestinal sacs. Confirming other reports, the potential difference in rat, hamster and guinea-pig preparations is significantly increased in the presence of sugars known to accumulate against a concentration difference. Also confirming other reports, the potential difference is strongly depressed with serosal ouabain and, to a lesser extent, also with mucosal ouabain in the absence of added sugar. However, it has now been additionally found that the increased potential difference in the presence of sugars as above, is still further enhanced by ouabain. This persistent effect of ouabain is species specific, being clearly evident in rat and, though of lesser intensity, also in guinea-pig, but not in hamster. In the rat the effect is observed with the sugars, d-glucose or 6-deoxy-d-glucose, in jejunal but not in ileal sacs and with d-galactose in ileal but not in jejunal sacs. Comparison of plots of i/ΔPD versusi/(sugar) in the presence and absence of ouabain suggests that ouabain acts as a competitive activator for Na⁺ entrance into the mucosal epithelial cell.