Once you isolate cDNA for the receptor involved in mediating heart contraction, you sub-clone the receptor cDNA in an expression plasmids and then stably transfect COS cells and pick the receptor-expressing COS-45 cell line. By using your receptor-expressing COS-45 cells, how would you show experimentally which the selective antagonist binds the receptor specifically? Discuss the experiment you would carry out and also the controls you would comprise.