Phosphate free medium

Wolfgang Schechinger wolfsc at ibms.sinica.edu.tw
Thu Mar 21 09:42:05 EST 2002


Dear Han, 

That methods reads interesting.

But are you sure that platelets can take up glucose*phosphate*? Then they'd 
have a unique and not yet described glucose(phosphate)transporter. And there 
would be the need for all these enzymes and intermediates you need to generate 
G6P *outside* the cells (starting with glucose and Pi).

Generally, 6-phosphorylation of glucose is considered to be the cellular 
method to "trap" glucose inside once it has come in through the glucose 
permeable pores (the glucose transporters). G6P won't be able to escape using 
the glucose transporters not flipflop or diffuse across the membrane because 
of it's charge. All known glucose transporters are pretty picky regarding 
their substrate, so they'll only let pass D-glucose but no G6P.

It seems to me in contrast that G6P becomes a significant storage for 
intracellular phosphate (respectively the cells immediately are in need of a 
lots of Pi) as soon as you overload the platelets with high glucose (5mM is 
approx 5 times (IIRC) higher than physiological). Thus they'll happily take up 
all phosphate you are offering to them in the media and thus you'll get a high 
uptake of 32Pi.

Regards, 

Wo

Han Broekman wrote:

> I had to use 32P in the late sixties to label platelet phospholipids. 
> Turned out labeling was most efficient (highest # of counts
> incorporated) when platelets were incubated in 2 mM Pi and 5 mM glucose,
> using the same number of counts.  Seems platelets "import" Pi as
> glucose-6-phosphate, and need extra phosphate around for that.  This was
> not a really exhaustive study, just one to find optimal conditions.  We
> eventually published the work, but I don't know the details by heart
> anymore.  See:

-----
Dr. Wolfgang Schechinger
Institute of Biomedical Sciences
Academia Sinica, Taipei, Taiwan

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