Sorbitol vs Glucose-6-phosphate - osmotically active?

[step1q]

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I understand that certain cells such as those in the lens contain aldose reductase and can use it to trap glucose in the cell in the form of sorbitol. During hyperglycemia there is alot of sorbitol in the cells which is osmotically active and causes swelling.

Why doesn't this happen in all cells - even those lacking aldose reductase? glocuse-6-phosphate is also osmotic, right?
I know hexokinase is inhibitted by glucose-6-phosphate which may be why not enough G6P builds up in a cell, but what about in organs like the liver with glucokinase?

 

[rashy]

I have the same question... why is sorbitol osmotically more active than glucose ??

 

[Charles_Carmichael]

My guess would be that it might be because G6P gets shunted into a metabolic pathway pretty quickly. For example, being shunted into the glycogenesis pathway and having the glucose added to an already existing glycogen polymer would increase the hepatocyte's glucose reserve without affecting osmolarity.

That's just my guess though.

 

[Suncrusher]

glucose can diffuse passively in and out of most cells--no gradient

G6P cannot diffuse out of cells, but as Kaushik said, it is quickly metabolized using one of many pathways--no gradient

sorbitol cannot diffuse in and out of cells. This leads to an osmotic gradient and swelling of the lens. Furthermore, according to my archives of PBL reports, one of my group members reported that some of the sorbitol will eventually be metabolized to fructose, resulting in increased AGE precursors and osmotic damage to nerves and myelinating Schwann cells, and also that both sorbitol and fructose play a role in decreasing Na/K pump activity somehow, which leads to further swelling...but I can't vouch for anything my group members said without looking it up the mechanisms myself