[Comparison of hydroelectrolytic exchange characterized by calculation of saturable fluxes at three levels of the rat intestine].

Using the everted sac technique, which responded, as expected, to VIP by an increase of the secretion and to glucose by an increase of the absorption, we compared the water and electrolyte movements in the jejunum, ileum and colon in rats. Identical iso-osmolar test-solutions containing increasing NaCl concentrations, placed on the serosal and mucosal sides, allowed us to quantify fluxes in the absence of initial gradient. The measured net Na and Cl fluxes were dissociated into their two components, a passive flux from serosa to mucosa and a saturable flux from mucosa to serosa. The parameters of the saturable transport, calculated for each of the intestinal parts, showed the highest J max for the ileum (58.5 microEq.g-1.h-1 for Na and 52.8 microEq.g-1.h-1 for Cl) and the lowest Km for the colon that had the highest affinity for sodium and chloride (Km 11.1 mM for Na and 7.8 mM for Cl). These data confirm the functional difference between the three intestinal parts, with an active absorption of Na and active secretion of Cl in the jejunum, an apparent coupled Na and Cl absorption in the ileum and an active absorption with high affinity for both Na and Cl in the colon.