Fig. 2. Erythropoietin receptor (EPO-R) protein levels in normal rat retina and retina after ischemic preconditioning (IPC). The levels in the contralateral, control, paired retinas were set to 100% (normalized) for comparison to the paired IPC retinae. (  A ) Densitometric analysis demonstrated no significant change in EPO-R levels at 1 and 6 h. A statistically significant increase was observed at 24 h for the 115-kD and 200-kD EPO-R. (  B ) Representative Western blot time course of EPO-R protein levels after IPC at 1, 6, or 24 h, demonstrating the increased levels of the differently sized EPO-R proteins after IPC. (  C ) Peptide competition assay shows that preincubation of the EPO-R antibody with specific blocking peptide results in no protein bands in normal whole retinal homogenates as compared to EPO-R antibody incubated with the phosphate-buffered saline (PBS) vehicle control. These results confirm that the multiple-sized bands seen with EPO-R Western blot are the EPO-R proteins.