21-BD regulates tight junctions.

MDCK cells were cultured in transwell permeable supports and treated with 5, 10 and 50 µM 21-BD. (A) TER was measured as a function of time. The control TER data (white circles, dotted line) averaged 183±8 Ω.cm2 (n = 13) and were normalized to 100%. 5 and 10 µM 21-BD provoke transient small increases of TER, while 50 µM 21-BD causes a stronger and a sustained TER increase (red circles). (B) MDCK cells were incubated 48 h with different concentrations of 21-BD (red symbols) or digoxin (green symbols). mRNA cell content of claudins -4 (circles) and -2 (triangles) were measured by quantitative real time PCR. (C) Protein cell content of the tight junction integral membrane proteins claudins -4 and -2 and the membrane-associated protein ZO-1 as a function of 21-BD concentration in the media for 48 h. Images from the left part of the figure C are representative immunoblots and the graph in the right part is the statistical analysis.