Modulation of intestinal paracellular permeability by intracellular mediators and cytoskeleton

The influence of cytoskeletal inhibitors (cytochalasin E and colchicine) and intracellular mediators (cAMP, Ca2+ and protein kinase C) in the control of paracellular permeability to mannitol has been examined in rat jejunum in Ussing-type chambers. Cytoskeletal inhibitors, cytochalasin E (20 mu mol.L-1) or colchicine (0.5 mmol.L-1), when present in mucosal, serosal, or in both mediums, significantly increase unidirectional mannitol fluxes. Exposure of mucosal and serosal intestinal surface to 10 mmol.L-1 theophylline or 1 mmol.L-1 cyclic AMP analogue for raising the intracellular cAMP enhances paracellular permeability. In Ca2+-free physiological medium passive permeability strongly increases. Alterations of cytosolic Ca2+ levels induced by the Ca2+ ionophore A23187 (20 mu mol.L-1) or by 0.3 mmol.L-1 TMB-8, a Ca2+ releasing inhibitor from the intracellular stores, enhance mannitol flux. Addition of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate, which activates protein kinase C (PKC), also induces a large increase in the intestinal permeability to mannitol. These results provide evidence that tight junctions and consequently epithelial paracellular permeability can be physiologically controlled by intracellular mediators (Ca2+, cAMP, and PKC) probably through modulation of the cytoskeleton activity.