Glucose entry into rat mesangial cells is mediated by both Na+-coupled and facilitative transporters

Abstract

Summary Since previous studies from our laboratory have demonstrated that increased glucose consumption by cultured rat mesangial cells is accompanied by an accelerated production of type IV and type VI collagen, we have now examined the manner by which glucose is transported into these cells. A progressive stimulation of glucose uptake by the mesangial cells was observed with increasing concentrations of NaC1 so that at 145 mmol/1 about twice as much glucose entered the cells as in its absence (substituted by choline chloride). Moreover, since phlorizin inhibited the NaCl-promoted uptake of glucose and this salt was found to increase the accumulation of c~-methylglucoside in a manner which could not be duplicated by KC1 or mannitol, both Na+-coupled and facilitative glucose transporters appeared to be present in the cells. K m values of 1.93 mmol/1 and 1.36 mmol/1 were determined for the co-transport and facilitated transport pathways, respectively, with their Vma X being 29.5 and 18.0 nmol. mg protein-1.h-1. Both uptake activities were found to be downregulated by exposure of the cells to high glucose and furthermore the Na+-dependent transport could no longer be detected after about 12 passages of the cells. Hybridization of mesangial cell mRNA with cDNA probes revealed transcripts for the Na+/glucose co-transporter as well as GLUT1 and to a lesser extent GLUT4. The identification of the co-transporter in these non-polarized cells is pertinent to an understanding of the intracellular signals which can lead to the development of the diabetic glomerular lesions; in the hyperglycaemic state this carrier provides an additional route for accelerated glucose entry and furthermore by the attendant increase in Na + flux may bring about an alteration in the ionic composition of the cell. [Diabetologia (1995) Although it has become evident that increased deposits of type IV as well as type VI collagen occur in the diabetic glomerulus [4,5] and that mesangial cells in culture demonstrate enhanced production of these two proteins in response to elevated glucose levels [6,7], the mechanism by which glucose and its metabolites regulate the synthesis of the glomerular extracellular matrix remains obscure. Only very limited information is currently available in regard to the manner of entry and subsequent metabolism of glucose by mesangial cells, a subject which is crucial to the understanding of the metabolic hypothesis of diabetic glomerulopathy.In an attempt to fill this void in knowledge and prompted by our recent observation that mesangial

Confocal microscopy study of the different patterns of 2-NBDG uptake in rabbit enterocytes in the apical and basal zone

“…To confirm this finding, we varied the activity of SGLT1 by exposing the enterocytes to different extracellular [Na + ] [15,16], an approach used successfully in rat mesangial cells and in renal brush-border vesicles of an early teleost [6,14]. We employed media with [Na + ] of 0.5, 100.5 or 130.5 mM; the [Na + ] could not be reduced further because Na-β-hydroxybutyrate is an essential requirement for enterocytes.…”

Glucose transporters in diabetic nephropathy

“…It is not yet known whether any of the other, more novel glucose transporters, including GLUT11, are expressed in glomerular cells. Finally, one group has identified sodiumglucose cotransporter (SGLT) activity in cultured mesangial cells [13]. However, there have been no additional studies reported to suggest that sodium-coupled glucose transport plays a major role in glucose uptake and metabolism in mesangial cells in culture or in vivo.…”

Molecular Genetic Approaches for Studying the Etiology of Diabetic Nephropathy

“…GLUT1 is the major facilitative glucose transporter in the glomerular mesangial cell [124]. Its overexpression in these cells creates a diabetic phenotype that includes features of excessive extracellular matrix production even when the cells were cultured under normoglycemic conditions [125,126].…”