Biochemistry and physiology of carbohydrates in the renal collecting duct.
Using 13C-NMR analysis of cell extracts, enzymatic determination of metabolites and cofactors as well as enzyme assays on cell homogenates aerobic and anaerobic glycolysis, sorbitol formation by aldose reductase, the pentose phosphate shunt, and gluconeogenesis could be identified as the major pathways of D-glucose metabolism in renal inner medullary collecting ducts. In flux studies it was shown that D-glucose enters the collecting duct cells via a sodium-independent, cytochalasin- and phloretin-inhibitable transport system located at the basal-lateral cell side. At the same side sorbitol leaves the cells during regulatory volume decrease in a calcium-calmodulin-dependent fashion. From cell isolation studies it is proposed that sorbitol is taken up by adjacent (interstitial) cells, converted into fructose and then recycled to the collecting duct cells. This cycle might prevent carbohydrate wasting. Thus, IMCD cells exhibit unique aspects of carbohydrate biochemistry and physiology which enable them to function in a surrounding of low oxygen tension, low substrate supply, and extreme changes in extracellular osmolality.
Kinne
R K
RK
Max-Planck-Institut für molekulare Physiologie, Abteilung Epithelphysiologie, Dortmund, Germany. daniela.maegdefessel@mpi-dortmund.mpg.de
Grunewald
R W
RW
Ruhfus
B
B
Kinne-Saffran
E
E
D000449:Aldehyde Reductase / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D050260:Carbohydrate Metabolism; D002478:Cells, Cultured; D066298:In Vitro Techniques; D007679:Kidney Medulla / Q000502:physiology; D007685:Kidney Tubules, Collecting / Q000737:chemistry* / Q000502:physiology*; D009682:Magnetic Resonance Spectroscopy; D051381:Rats; D013012:Sorbitol / Q000378:metabolism; D014882:Water-Electrolyte Balance / Q000502:physiology
D013012:Sorbitol; D000449:Aldehyde Reductase