The bivalence of juxtaglomerular cells in the maturing rat kidney. A comparative study of secretory and contractile potential.

A comparative immunofluorescence and light microscopical study of the three cell types of the juxtaglomerular apparatus (pure muscle cells, pure granular cells and mixed cells) was performed on the growing and maturing kidney of the rat. Mixed cells, containing contractile protein and secretory granules, are detectable on the first postnatal day in about one third of the JGAs. From the third week, the number of bivalent cells increases, while the proportion of pure muscle or pure granular cells decreases. Morphological and functional maturation, achieved by 3 to 4 weeks, is associated with increasing numbers of bivalent cells and a shift in the main site of renin production from the inner to the outer cortical zone. The divergent internal structure of JGA cell types expresses the range of varied differentiation expressed by one cell line. Pure muscle or granular cells are at the extremes of the range and mixed cells take up an intermediate position.