Aldosterone and tight junctions:: modulation of claudin-4 phosphorylation in renal collecting duct cells

Aldosterone classically modulates Na transport in tight epithelia such as the renal collecting duct ( CD) through the transcellular route, but it is not known whether the hormone could also affect paracellular permeability. Such permeability is controlled by tight junctions ( TJ) that form a size- and charge- selective barrier. Among TJ proteins, claudin-4 has been highlighted as a key element to control paracellular charge selectivity. In RCCD2 CD cells grown on filters, we have identified novel early aldosterone effects on TJ. Endogenous claudin- 4 abundance and cellular localization were unaltered by aldosterone. However, the hormone promoted rapid ( within 15 - 20 min) and transient phosphorylation of endogenous claudin- 4 on threonine residues, without affecting tyrosine or serine; this event was fully developed at 10 nM aldosterone and appeared specific for aldosterone ( because it is not observed after dexamethasone treatment and it depends on mineralocorticoid receptor occupancy). Within the same delay, aldosterone also promoted an increased apical- to- basal passage of I-125 ( a substitute for Cl-36), whereas Na-22 passage was unaffected; paracellular permeability to [H-3] mannitol was also reduced. Later on ( 45 min), a fall in transepithelial resistance was observed. These data indicate that aldosterone modulates TJ properties in renal epithelial cells.