Effect of Tat on the Transepithelial Electrical Resistance in D407 cells. (a): From 2 days after seeding, the TER was measured every other day to monitor the time course of the TER of D407 cells. The TER gradually increased, peaking at day 8 and then remaining stable for 1 week. Values shown represent the mean ± S.D. of three independent assays or experiments. (b): The effects of 100 nM the Tat on TER of D407 cells were measured at 1, 2, 3, 12, 24, 48, and 72 hours after stimulation. The TER values were stable in the control group (□) and heat-inactivated group (▲) throughout the experiment, with no significant differences between them. However, treatment with 100 nM Tat(■) induced a significant decrease in the TER beginning at 3 hours, with a further decrease at 12 hours and a maximum effect at 24 hours, which was maintained to 72 hours. Values shown represent the mean ± S.D. of three independent assays or experiments. (* P < 0.05, # P < 0.01).