The kidneys play a major role in the regulation of glucose levels.
Kidneys filter approx.
180g of glucose per day from the blood, and this is mostly reabsorbed back into the blood in the proximal tubules.
Typically, glucose is first absorbed within epithelium by a specific transporter protein, Sodium glucoseco transporters (SGLT), in the brush-border membrane and then it is transported out of the cell across the basolateral membranes by a facilitated sugar transporter (GLUTs).
At least 3 members of SGLTs (SGLT1-3) have been cloned and characterized from various species.
Individual member of this family have identical predicted secondary structures with up to 14 transmembrane domains.
SGLT1-3 genes code for protein of approx 659-672 residues (calculated size of ~75kD).
Both N and C-termini are predicted to be extracellualr.
There is approx 60-70% homology between SGLT1-3.
SGLTs transport a-methyl-D-glucoside (a-MDG), a non-metabolized model substrate, in Na-dependent manner.
SGLT1 does not discriminate a-MDG, glucose, and galactose.
SGLT2/3 do not transport D-galactose efficiently.
SGLT1/NAGT or SLC5A1/NAGT (rat/mouse 665aa; human 664aa, chromosome 22q13.1, ~75kD) is a high affinity, Na+-coupled, intestinal responsible for active glucose transport across the brush border membrane.
In the kidney, SGLT1 is expressed in proximal tubule Sq1 segments.
It is also expressed in the intestine.
Defects in SGLT1 gene have been implicated in congenital glucose-galactose malabsorption syndrome (GGM).
SGLT2/SLC5A2 (rat/mouse 670aa; human 672aa, chromosome 16p11.2) is the low affinity, high capacity Na+-glucose transporter located in the S1 segments of proximal tubules.
It is ~60% identical with SGLT1.
SGLT2 mediates saturable Na-dependent and phlorizin-sensitive glucose transport.
In contrast with SGLT1, SGLT2 does not transport D-galactose.
Defect in SGLT2 may be associated with renal glycosuria.
SGLT3/SLC54 (porcine 660aa; mouse 656/660/616aa; human 659aa, chromosome 22), originally named SAAT1 or pSGLT2, was initially identified in LLC-Pk1 cell line derived from porcine renal epithelium.
It is also low affinity Na-glucose transporter.
It is expressed in kidney, intestine, liver, skeletal muscle and spleen.
Like SGLT2, SGLT3 has a low affinity for sugars, and is highly selective for D-glucose and low affinity for D-galactose.
Applications:Suitable for use in ELISA.
Western Blot, though not tested, may potentially be used as an application.
