Immortalized murine hepatocytes - (Sep/11/2009 )

I've immortalized hepatocytes from neonate Black 6 mice. I'm culturing them in DMEM plus 10%FCS and hormones(insulin, dexamethasone, EGF). To show that they are indeed hepatocytes, I'm looking at albumin synthesis. I find albumin in the medium but when I lyse the cells with RIPA buffer, I only find a band at ~120,000kDa, not at 66,000kDa where the albumin migrates.
Is it the medium; is it the RIPA lysing buffer?
PS They don't look like your normal hepatocytes.

Occam's razor says that the simplest answer is usually the correct one... Perhaps they aren't hepatocytes. I would do some morphology and histochemistry for cell specific markers to make sure that they are hepatocytes.