Figure 2 - Effect of the endocytocis inhibitor, phenylarsine oxide (PAO), on the cell surface distribution of bound fluo-dermorphin. COS-7 cells transfected with cDNA encoding the mu opioid receptor were incubated for 45 min, at 37oC, with 10 nM fluo-dermorphin in the presence of 10 ÁM PAO. Note how the bound fluorescent molecules form a single large cluster at one pole of the cell (arrow). Scale bar: 5 Ám.