Claudins and paracellular transport: an update.
OBJECTIVE
Claudins are tight junction proteins that form paracellular barriers and pores. The purpose of this timely review is to provide an update on the exciting new advances in our understanding of claudin biology and their relevance to renal physiology and pathophysiology.


RESULTS
Accumulating evidence from numerous studies indicates that the primary role of claudins is to determine the permeability and charge selectivity of the paracellular pathway to small ions. Studies in which claudins are overexpressed in cell lines have potential limitations and need to be interpreted cautiously. Ribonucleic acid interference is a novel approach to functional characterization. Claudins are believed to assemble into multimers by homophilic and heterophilic side-by-side and head-to-head interaction; however, there is still limited evidence for this. The roles of a few claudins in the renal tubule, including claudins 2, 8, 10, 16 and 19, have now been elucidated.


CONCLUSIONS
These findings reveal tantalizing clues to claudin biology and function. Much remains unknown, however, and these findings will hopefully encourage further research in this important area.
Angelow
Susanne
S
Division of Nephrology, Department of Medicine, University of Southern California Keck School of Medicine, Los Angeles, California 90033, USA.
Yu
Alan S L
AS
D000818:Animals; D001692:Biological Transport; D062445:Claudin-1; D004285:Dogs; D006801:Humans; D007477:Ions; D007684:Kidney Tubules / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000502:physiology*; D008954:Models, Biological; D011485:Protein Binding; D020033:Protein Isoforms; D034622:RNA Interference; D013552:Swine; D019108:Tight Junctions / Q000378:metabolism*
C568108:CLDN1 protein, human; D062445:Claudin-1; D007477:Ions; D008565:Membrane Proteins; D020033:Protein Isoforms