Water transport through the sodium-glucose cotransporter SGLT1

Description

The intestine reabsorbs about nine liters of water daily. A primary role in that water uptake has been ascribed to secondary active transporters that are thought to couple water transport to sodium transport along its concentration gradient. In contrast, homology structure-based molecular dynamics simulations suggest passive water movement through the most prominent member of the water transporting carrier family, the sodium-glucose cotransporter SGLT1. However, their calculated turnover numbers are three to four orders of magnitude higher than those determined experimentally. To clarify the water transporting mechanism of SGLT1, we used a previously established assay for determining the single molecule water permeability, pf , for transporters in epithelial cell monolayers. That is, we measured the dilution of an aqueous dye in the immediate vicinity of the monolayer and determined the abundance of the EGFP-tagged SGLT1 transporter in the apical and basolateral membranes by fluorescence correlation spectroscopy. The pf value compares well to that reported for aquaporins. It indicates the presence of a passive water channel and is thus not compatible with secondary active water transport. We obtained independent proof by reconstituting the purified SGLT1 into lipid vesicles.

Period	21 Jul 2015
Event title	10th European Biophysics Congress
Event type	Conference
Location	GermanyShow on map