Using xanthine in cell culture media?

[Helen Cheng]

Hello,

I have a question about adding xanthine to cell culture media (for
XGPRT selection).  I make up 100x stock soln of xanthine in 1 M NaOH
and add this
to MEM + HAT media....the problem is that xanthine comes out of
solution very 
easily at pH's below 8-9, so when I add my xanthine to the media, it
becomes
slightly hazy.  Does anyone know what the proper way to make up
xanthine-containg media is?  (I would like to use it at the standard
0.25 mg/ml final concentration).

I appreciate any help! Thanks.


Helen Cheng
hhc at leland.stanford.edu