STIMULATING EFFECTS OF SORBITOL ON ILEAL CALCIUM-TRANSPORT IN IN-SITUPERFUSED LOOP IN RATS

Objectives. - The aim of this study was to study the effect of sorbito l on sodium, water and calcium fluxes in rat ileum in situ perfused lo op. Methods. - Net water; sodium and calcium fluxes, and one-way calci um fluxes were measured in situ in a perfused rat ileal loop in the pr esence of varying concentrations of sorbital. Results. - High concentr ations of sorbitol in perfused ileal solution induced a decrease of so dium and water fluxes and a concomitant increase of lumen to mucosa ca lcium flux associated with an increase of net calcium flux, using a so lution containing either 8.0 or 1.25 mM calcium. These effects were in dependent of absolute initial values of water and sodium fluxes. They were observed in the presence of 25 mM glucose, 10 mM theophyllin or a fter treatment of rats with dexamethasone. Conclusion. - These effects of sorbitol on calcium flux are not compatible with a stimulation of paracellular pathway. By contrast, they can be explained by a stimulat ion of transcellular calcium pathway in ileum associated with the hype rpolarisation of the cells induced by the decrease of luminal sodium c oncentration necessary in the presence of sorbitol to maintain unchang ed osmolarity of perfusate.