if the cell media is with calf serum you will have trouble with the serum albumin (lot of it on the gel....) for the control it depends what you want to see: medium without cells can be an option....

Dear Didier Poncet thank you for your answer.

I am trying to see if my cells secrete proteins such as TDP43. My medium does not contain albumin nor FBS.

so if you have no FBS in your culture medium you will be eventually also able to concentrate it. Your control could be medium which has not been use to grow cells or the same medium used to grow cells that you know are not expressing the TDP43.

Dear Didier Poncet thank you very much!