Role of NO in the Function of the Juxtaglomerular Apparatus

Abstract

Juxtaglomerular apparatus (JGA) is the anatomical term for a conglomeration of specialized cells positioned at the vascular pole of the renal glomerulus. The constituents of this cell complex are epithelial, interstitial, and modified smooth muscle cells. The epithelial cells of the JGA are located at the distal end of the thick ascending limbs, a part of the nephron that always returns to the vascular pole of its parent glomerulus. The tubular cells in this contact area, called the macula densa (MD) cells, are cytologically distinct from the surrounding thick ascending limb cells. Underlying the MD cell plaque and filling the space between it and the arterioles is a cushionlike complex of specialized interstitial cells, called the extraglomerular mesangium (EGM). In their fine structure, EGM cells are similar to intraglomerular mesangial cells. EGM cells are coupled by an extensive network of gap junctions with each other. They are also coupled with vascular smooth muscle cells in the afferent arteriole and with the renin-containing granular cells in the media of the arteriolar wall. This anatomical arrangement is the probable route for a communication pathway along which changes in tubular fluid composition in the tubular lumen at the macula densa initiate successive alterations in the functional state of MD cells, EGM cells, and, finally, vascular smooth muscle and granular cells.