Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 291, Issue 18, Pages 9712-9720Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M115.706986
Keywords
-
Categories
Funding
- Austrian Science Fund [P23574]
- Austrian Science Fund (FWF) [P23574] Funding Source: Austrian Science Fund (FWF)
- Austrian Science Fund (FWF) [P 23574] Funding Source: researchfish
Ask authors/readers for more resources
The small intestine is void of aquaporins adept at facilitating vectorial water transport, and yet it reabsorbs similar to 8 liters of fluid daily. Implications of the sodium glucose cotransporter SGLT1 in either pumping water or passively channeling water contrast with its reported water transporting capacity, which lags behind that of aquaporin-1 by 3 orders of magnitude. Here we overexpressed SGLT1 in MDCK cell monolayers and reconstituted the purified transporter into proteoliposomes. We observed the rate of osmotic proteoliposome deflation by light scattering. Fluorescence correlation spectroscopy served to assess (i) SGLT1 abundance in both vesicles and plasma membranes and (ii) flow-mediated dilution of an aqueous dye adjacent to the cell monolayer. Calculation of the unitary water channel permeability, p(f), yielded similar values for cell and proteoliposome experiments. Neither the absence of glucose or Na+, nor the lack of membrane voltage in vesicles, nor the directionality of water flow grossly altered p(f). Such weak dependence on protein conformation indicates that a water-impermeable occluded state (glucose and Na+ in their binding pockets) lasts for only a minor fraction of the transport cycle or, alternatively, that occlusion of the substrate does not render the transporter water-impermeable as was suggested by computational studies of the bacterial homologue vSGLT. Although the similarity between the p(f) values of SGLT1 and aquaporin-1 makes a transcellular pathway plausible, it renders water pumping physiologically negligible because the passive flux would be orders of magnitude larger.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available