FRUCTOSE REABSORPTION BY RAT PROXIMAL TUBULES: ROLE OF SODIUM-LINKED COTRANSPORTERS AND THE EFFECT OF DIETARY FRUCTOSE

FRUCTOSE REABSORPTION BY RAT PROXIMAL TUBULES: ROLE OF SODIUM-LINKED COTRANSPORTERS AND THE... Fructose consumption has increased due to widespread use of high-fructose corn syrup by the food industry. Renal proximal tubules are thought to reabsorb fructose. However, fructose reabsorption (Jfructose) by proximal tubules has not yet been directly demonstrated, nor the effects of dietary fructose on Jfructose. This segment express sodium-glucose linked transporters (SGLTs) 1, 2, 4 and 5, and glucose transporters (GLUTs) 2 and 5. SGLT4 and 5 transport fructose but SGLT1 and 2 don't. Knocking out SGLT5 increases urinary fructose excretion. We hypothesize that Jfructose in the S2 portion of the proximal tubule is mediated by luminal entry via SGLT4/5 and basolateral exit by GLUT2, and that it is enhanced by a fructose-enriched diet. We measured Jfructose by proximal straight tubules from rats consuming either tap water (Controls) or 20% fructose (FRU). Basal Jfructose in Controls was 14.1±1.5 pmol/mm/min. SGLT inhibition with phlorizin reduced Jfructose to 4.9±1.4 pmol/mm/min (p<0.008), while removal of Na diminished Jfructose by 86±5% (p<0.0001). A fructose-enriched diet increased Jfructose from 12.8 ± 2.5 to 19.3±0.5 pmol/mm/min, 51% increase (p<0.03). Using immunofluorescence, we detected luminal SGLT4 and SGLT5 and basolateral GLUT2; GLUT5 was undetectable. The expression of apical transporters SGLT4 and SGLT5 was higher in FRU than in Controls; 137±10% (p<0.01) and 38±14% (p<0.04) respectively. GLUT2 was also elevated by 88±27% (p<0.02) in FRU. We conclude that Jfructose by proximal tubules occurs primarily via sodium-linked cotransport processes and a fructose-enriched diet enhances reabsorption. Transport across luminal and basolateral membranes is likely mediated by SGLT4/5 and GLUT2, respectively. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png American Journal of Physiology-Renal Physiology The American Physiological Society

FRUCTOSE REABSORPTION BY RAT PROXIMAL TUBULES: ROLE OF SODIUM-LINKED COTRANSPORTERS AND THE EFFECT OF DIETARY FRUCTOSE

American Journal of Physiology-Renal PhysiologyMay 22, 2018

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/lp/the-american-physiological-society/fructose-reabsorption-by-rat-proximal-tubules-role-of-sodium-linked-mnR0qAmnH1
ISSN
1931-857x
eISSN
1522-1466
D.O.I.
10.1152/ajprenal.00247.2018
Publisher site
See Article on Publisher Site

Abstract

Fructose consumption has increased due to widespread use of high-fructose corn syrup by the food industry. Renal proximal tubules are thought to reabsorb fructose. However, fructose reabsorption (Jfructose) by proximal tubules has not yet been directly demonstrated, nor the effects of dietary fructose on Jfructose. This segment express sodium-glucose linked transporters (SGLTs) 1, 2, 4 and 5, and glucose transporters (GLUTs) 2 and 5. SGLT4 and 5 transport fructose but SGLT1 and 2 don't. Knocking out SGLT5 increases urinary fructose excretion. We hypothesize that Jfructose in the S2 portion of the proximal tubule is mediated by luminal entry via SGLT4/5 and basolateral exit by GLUT2, and that it is enhanced by a fructose-enriched diet. We measured Jfructose by proximal straight tubules from rats consuming either tap water (Controls) or 20% fructose (FRU). Basal Jfructose in Controls was 14.1±1.5 pmol/mm/min. SGLT inhibition with phlorizin reduced Jfructose to 4.9±1.4 pmol/mm/min (p<0.008), while removal of Na diminished Jfructose by 86±5% (p<0.0001). A fructose-enriched diet increased Jfructose from 12.8 ± 2.5 to 19.3±0.5 pmol/mm/min, 51% increase (p<0.03). Using immunofluorescence, we detected luminal SGLT4 and SGLT5 and basolateral GLUT2; GLUT5 was undetectable. The expression of apical transporters SGLT4 and SGLT5 was higher in FRU than in Controls; 137±10% (p<0.01) and 38±14% (p<0.04) respectively. GLUT2 was also elevated by 88±27% (p<0.02) in FRU. We conclude that Jfructose by proximal tubules occurs primarily via sodium-linked cotransport processes and a fructose-enriched diet enhances reabsorption. Transport across luminal and basolateral membranes is likely mediated by SGLT4/5 and GLUT2, respectively.

Journal

American Journal of Physiology-Renal PhysiologyThe American Physiological Society

Published: May 22, 2018

References

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