Wasted salts and wasted bodies: new insight into the role of claudin 7 in the kidney

IN MULTICELLULAR ORGANISMS, epithelial sheets function as a barrier between two compartments via their ability to form tight junctions (TJs), which regulate the diffusion of fluid, electrolytes, and small molecules through the paracellular path-way. Members of the relatively recently described Claudin (Cldn) family of integral membrane proteins, with at least 23 distinct members in mammals, are the major structural and functional components of TJ strands and are considered to be the best candidates for forming paracellular channels (3, 4, 6, 15). Similarities and differences between Cldn family members and their diverse expression patterns are thought to provide the molecular basis for the hetereogeneous features of the paracel-lular permeability barriers, including differences in the degree of “tightness ” and ion selectivity, manifested in different tis-sues and organs