Hi, I have been performing 3-4 cell based assays with rat heart H9C2 cells since last 6 months, and I have a lot of trouble with the reproducibility of data. I have been culturing cells as per ATCC protocol, and not letting them grow to confluency. Still, the data for the assays I perfomed is variable. Sometimes cells are responding to the treatment, sometimes not. Does anyone face similar problem? Please help.