COMPARISON OF HYDROELECTRIC EXCHANGES CHA RACTERIZED BY THE CALCULATION OF SATURABLE FLOWS IN THE JEJUNUM, ILEUM AND COLON OF THE RAT

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 a bsorption, we compared the water and electrolyte movements in the jeju num, ileum and colon in rats. Identical iso-osmolar test-solutions con taining increasing NaCl concentrations, placed on the serosal and muco sal sides, allowed us to quantify fluxes in the absence of initial gra dient. The measured net Na and Cl fluxes were dissociated into their t wo components, a passive flux from serosa to mucosa and a saturable fl ux from mucosa to serosa. The parameters of the saturable transport, c alculated for each of the intestinal parts, showed the highest J max f or the ileum (58.5 mu Eq.g(-1).h(-1) for Na and 52.8 mu Eq.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 pa rts, 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.