Giant renin secretory granules in beige mouse renal afferent arterioles

Abstract.

The mutant beige mouse (C57BL/6 bg) has a disease characterised by abnormally enlarged cytoplasmic granules in a variety of cells. With the purpose of establishing a suitable cellular model for studying renin secretion, the present study was undertaken to compare renin granule morphology in beige mice with that of control (NMRI) mice. Immunohistochemistry with an antibody specific for renin revealed intense staining of the juxtaglomerular part of the afferent arterioles in both strains of mice. Plasma renin concentrations were higher in the controls than in the beige mice (4.4±0.6 vs 2.5±0.3 mGoldblatt units/ml). The total volume of renin granules per afferent arteriole was similar in the two mice strains (1114 μm³ in the controls and 1507 μm³ in the beige mice). The total number of renin granules per arteriole as assessed by stereological techniques was about 1900 in controls (average granular volume 0.681 μm³), whereas 1–2 large granules were present per cell in beige mice. The volume of afferent arteriole that contained secretory granules was lower in the beige mice. We conclude that the beige mouse synthesizes, stores and releases active renin. Renin secretory granules in beige mice are grossly enlarged with 1–2 granules per juxtaglomerular cell. Compared with control mice, a similar amount of total renin granule volume per afferent arteriole is contained in a smaller part of beige mouse afferent arteriole. Granular cells from beige mice could therefore be a valuable tool in the study of renin release.