Hello!

I isolate cardiomyocytes and treat them , then fix them Acetone:Methanol for 20 mins -20C and permeabilize the cells with Triton. I block by PBS with 5% BSA for 45 mins then use Sigma Mouse Desmin primary Antibody (IgG)1:50 concentration and Anti Mouse IgG Alexa 488 secondary antibody 1:1000 for staining. 

Hi Ketaki,

May be  weak staining indicating the low expression of Desmin after your treatment of cardiomyocytes.

Also sometimes methanol due to auto florescence subside antibody signal. You can increase concentration of primary antibody or try antibody from different company. Best of Luck.