MTT assay overactivity - (Sep/12/2011 )

Now, I do MTT assay in pulp cells (Pulp medium consist of alpha - MEM , L- glutamine, ascorbic acid, Fungizone , Penstrep and fetal bovine serum). But the problem that when I incubate 10 mM HEPES in pulp medium and MTT in blank well (No cell),After 3 hr , Remove all solution and dissolve with DMSO. There is dark purple color. Then , The experiment groups are low OD because the blank gr is high OD. I change new pulp media but it 's not better.Can anyone explain the problem like this?

I do this assay before it's no any ploblem.

Don't you add anything in your medium that might react with the MTT salt.

MTT is normally reduced by succinate dehydrogenase. That is to say that MTT is the oxidized form of formazan.
As any oxidizer, MTT can react with reducers (e.g antioxidant...)