Fig. 5. Effect of claudin-7 overexpression on TER in modified P1 buffer. (A) TER measurements were performed on LLC-PK1 cells grown on Transwell plates. 140 mM NaCl in P1 buffer was replaced by 140 mM arginine-HCl. In the solution, HCl dissociated into H⁺ and Cl^–, and H⁺ bound to OH^– in the solution to form water at pH 7.3. Without Na⁺ in the solution, TER was dramatically increased in cells overexpressing claudin-7 (2) compared to that of control cells (P<0.001). (B) The experimental condition was similar to that in A, but 140 mM NaCl was substituted by 140 mM lysine-HCl. A significant increase in TER was also observed in cells overexpressing claudin-7 (2) (P<0.001). (C) In contrast, TER significantly decreased (P<0.01) in claudin-7-overexpressing cells when 140 mM NaCl was replaced with 140 mM sodium aspartate (2). Data were obtained from at least three mixed clones (n=24 for each experiment) and presented as means ± s.e.m.