Figure 1. The transepithelial electrical resistance (TER) of cultured RPE is affected by serum and embryonic day 14 (E14) retinal conditioned medium (rcSF3). RPE was isolated from E7 or E14 cultures and cultured in control media (SF3, defined in the Methods, in the apical medium chamber and SF2, defined in the Methods, in the basal chamber) or with the following modifications: In some cultures, the basal media was supplemented with 2% FBS (indicated by “serum”). In some cultures, the apical medium replaced by retinal conditioned medium (indicated by rcSF3). Each data point is the average of 6–9 cultures. The standard error was smaller than the symbols.