Figure 1. SCF/cKit signaling induces retinal vascular hyperpermeability. A: Stem cell factor (SCF) increases the endothelial permeability of human retinal microvascular endothelial cells (HRMECs) with potency comparable to that of vascular endothelial growth factor (VEGF). Endothelial permeability was determined by measuring the transendothelial electrical resistance (TEER) in the HRMEC monolayer after 30-min incubation with PBS, rh SCF (50 ng/ml), or rh VEGF (50 ng/ml; *p<0.05 versus PBS, n = 5). B: Imatinib mesylate inhibits SCF-induced hyperpermeability of HRMECs. TEER was measured in HRMECs that were pretreated with 10 μM imatinib mesylate for 30 min before stimulation with rh SCF (50 ng/ml; *p<0.05 versus PBS, n = 5). C: SCF increases the retinal vascular leakage in the wild-type (WT) mice but not in the cKit mutant (Kit^w-sh/w-sh) mice. Retinal vascular permeability was determined using Evans blue (EB) dye in the WT and Kit^w-sh/w-sh mice, which were intravitreously injected into each eye with PBS or rm SCF (50 ng in 1 μl of PBS; *p<0.5, ns = not significant, n = 4).