Why is SGLT1 Active Transport?

[Mushrooomboy]

Hi I've been reviewing the GLUT transporters and I don't understand why SGLT1 is an secondary active transporter if it's just bringing glucose from the intestinal lumen into the epithelial cells in the gut. Isn't [glucose] higher in the gut lumen because of the food we ate? If so, why do we need to couple SGLT1 to a Na/K ATPase to transport glucose?

Any help would be great, thanks!

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[sovereign0]

Hi I've been reviewing the GLUT transporters and I don't understand why SGLT1 is an secondary active transporter if it's just bringing glucose from the intestinal lumen into the epithelial cells in the gut. Isn't [glucose] higher in the gut lumen because of the food we ate? If so, why do we need to couple SGLT1 to a Na/K ATPase to transport glucose?

Any help would be great, thanks!

It's secondary active transport because the import of glucose isn't directly coupled to the hydrolysis of ATP, rather, it's coupled to the Sodium concentration gradient.

I think that glucose is unable to be passively transported because, while there is a concentration gradient, glucose is too large and polar to be able to diffuse through the membrane or take advantage of a channel. There may be exceptions, but I believe that most larger molecules and most peptides require some kind of active transport mechanism for transport through the membrane. Channels seem to predominantly work with ions.

 

[Mushrooomboy]

You're right but my question is if [glucose] is high in the gut lumen, why doesn't it just undergo facilitated diffusion to enter the cell like with the GLUT transporters? The GLUT transporters transport glucose into epithelial cells bc [glucose] in blood is always higher than [glucose] in the epithelial cells. Unless [glucose] is low in the gut lumen? Does anyone know?

It's secondary active transport because the import of glucose isn't directly coupled to the hydrolysis of ATP, rather, it's coupled to the Sodium concentration gradient.

I think that glucose is unable to be passively transported because, while there is a concentration gradient, glucose is too large and polar to be able to diffuse through the membrane or take advantage of a channel. There may be exceptions, but I believe that most larger molecules and most peptides require some kind of active transport mechanism for transport through the membrane. Channels seem to predominantly work with ions.

 

[68PGunner]

You're right but my question is if [glucose] is high in the gut lumen, why doesn't it just undergo facilitated diffusion to enter the cell like with the GLUT transporters? The GLUT transporters transport glucose into epithelial cells bc [glucose] in blood is always higher than [glucose] in the epithelial cells. Unless [glucose] is low in the gut lumen? Does anyone know?

The role of SGLT1 and GLUT2 in intestinal glucose transport and sensing. - PubMed - NCBI

The answer is that it doesn't happen.