A molecular look at the glomerular barrier.

The glomerular barrier is the kidney's physical block to the unrestricted flow of molecules from the plasma into the urinary space. Its exquisite selectivity allows solutes and water in the glomerular capillaries to pass through, but it prevents the bulk of plasma proteins, most notably albumin, from crossing. Classically, the barrier consists of three distinct components: glomerular endothelium, glomerular basement membrane, and glomerular epithelium (podocytes). In this review, I discuss these three components, with particular emphasis on the barrier presumed to be imparted by a specialized podocyte cell-cell junction, the glomerular slit diaphragm.