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Size dependence of paracellular flux (solid black line) indicates the presence of two pathways. (A) A high-capacity pore pathway (dashed green line) is responsible for trans-tight junction flux of small ions and molecules, whereas a leaky pathway (dashed red line) allows paracellular flux of larger molecules (after Refs. 14, 16, and 17). (B) Claudins primarily regulate the pore pathway, while occludin appears to be important to leak pathway regulation (after Ref. 29).15,17,28
