ObjectiveTo observe the stoichiometry of vascular endothelial growth factor receptor 2 (VEGFR2) on the retinal vascular endothelial cell membrane by single-molecule fluorescence imaging.MethodsRhesus monkey retinal vascular endothelial cells (RF/6A) were divided into blank control group (normal culture) and plasmid transfection group [transfected with VEGFR2-green fluorescent protein (GFP) recombinant plasmid]. The expression of GFP in the plasmid transfected group was observed by confocal microscope, and the expression of VEGFR2 in the cells was detected by real-time fluorescent quantitative polymerase chain reaction (qPCR) and Western blot. The fluorescence intensity distribution and bleaching steps of single VEGFR2-GFP molecule on the cell membrane were recorded by single-molecule imaging. The distribution of fluorescence intensity and the number of fluorescence bleaching steps of GFP were recorded.ResultsGFP green fluorescence was observed in the transfected cells 12 hours after transfection. qPCR results showed that the expression of VEGFR2 and GFP mRNA in the plasmid transfected group was significantly higher than that in the blank control group (t=11.240, 12.330; P＜0.001, 0.001). Western blot results showed that the expression of VEGFR2 protein in the plasmid transfected group was significantly higher than that in the blank control group (t=8.346, P＜0.01). The results of single-molecule imaging showed that the fluorescence intensity distribution of VEGFR2-GFP on the surface of RF/6A cell membrane without ligand stimulation was bimodal, in which monomer and dimer were 86.0% and 14.0% respectively. By counting the steps of GFP fluorescence bleaching, the proportions of receptor monomer, dimer, trimer, and tetramer were 81.4%, 12.9%, 5.5%, and 0.3% respectively.ConclusionIn the absence of ligands, VEGFR2 coexists in the form of monomers and dimers on the surface of RF/6A cell membrane, and monomers are dominant.