REGULATION OF INTESTINAL NA ABSORPTION

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DESCRIPTION (provided by applicant): Better insight into the regulation of the two primary Na absorptive pathways in the mammalian small intestine, Na:H exchange (NHE3) and Na-glucose co-transport (SGLT1), is necessary to develop more efficacious treatments for a variety of common medical conditions (e.g. diarrheal diseases, hypertension, diabetes, obesity). NHE3 mediates coupled NaCl absorption via the dual operation of Na:H and Cl:HCO3 exchange while SGLT1 is important to assimilate Na and glucose on the brush border membrane (BBM) of absorptive villus cells . The regulation of both by nitric oxide (NO), one of the most biologically active molecules, was unclear. We reported that in vivo and in vitro inhibition of constitutive NO (cNO) resulted in the inhibition SGLT1 but the stimulation of NHE3. In contrast, stimulation of cNO resulted in the stimulation of SGLT1 and inhibition of NHE3. Thus, our data indicate that BBM NHE3 and SGLT1 may be compensatorily regulated by NO to maintain cellular Na homeostasis. This then led to our novel overall hypothesis that the major Na absorptive pathways, NHE3 and SGLT1, regulate one another to maintain cellular Na homeostasis in epithelial cells likely via NO. The overall aim that will address this hypothesis will be to determine how permanent silencing of SGLT1 or NHE3 stimulates the other transporter and define the cellular and molecular mechanisms likely mediated by cNO. The results of this study will provide significant and new mechanistic insight into whether and how SGLT1 and NHE3 directly regulate one another. These resulting novel insights may form the basis for developing novel strategies to promote electrolyte and nutrient absorption where deficient and inhibit the same in disease states where it would be advantageous to do so.