Claudin-15 forms a water channel through the tight junction with distinct function compared to claudin-2.

Claudin-15, similar to claudin-2, forms a paracellular cation and water channel. In functional contrast to claudin-2, water and Na+ fluxes through claudin-15 inhibit each other. Claudin-15 allows Na+ to retain part of its hydration shell within the pore. This then reduces the simultaneous passage of additional water through the pore.