Regional variation of energy sources in intestinal phosphate transport using everted gut sacs of mice

Background & Aim: The transcellular transport of phosphate (Pi) from the intestinal lumen to the blood is documented as a secondary active transport requiring energy. In renal tubules the source of ATP generation for Pi transport seems to vary with site of transport. As studies are not available showing energy sources of intestinal Pi transport an attempt is done in this study to explore the metabolic energy source related to intestinal Pi transport. Methods: Everted gut sacs of the proximal & distal intestine were prepared from Swiss male albino mice. The sacs were filled with 0. 5ml of serosal fluid and placed in a mucosal medium. Various metabolic blockers of glycolysis and oxidative phosphorylation like 2DG, monoiodoacetate and rotenone were added to the incubation medium to curtail the energy sources. Tricarboxylic acid intermediates, Succinate and fumarate were also used in the medium to stimulate ATP generation. After incubation of the filled sacs for an hour, the amount of phosphate removed from mucosal medium (Pi uptake) and serosal gain of phosphate (Pi release) were estimated according to Chen’s method. Results: In these experiments phosphate uptake remains unaffected in both proximal and distal everted gut sacs with varied metabolic blockers. However addition of 2DG and monoiodoacetate significantly (<.001) reduced Pi release from the proximal segments without affecting Pi release in distal segments. Rotenone significantly (<.001) lowered Pi release in distal segments only without affecting the proximal segments. Inhibitory effect of rotenone on Pi release of the distal segments was partly but significantly checked by succinate and fumarate. Conclusion: Present studies indicate that the process of Pi extrusion/release from basolateral membrane only requires energy. For Pi release proximal intestine depend on glycolysis and distal part depend on oxidative phosphorylation for energy showing the regional variation.