Synthesis and Traffic of Renin in Epithelioid Cells

Abstract

In cell types with regulated secretion, the concentration and/or packaging of the secretory product occurs in specialized Golgi-dependent condensing vacuoles or in the transmost Golgi cistern (for review see Farquhar and Palade 1981; Farquhar 1985). Barajas and Latta (1965) and Barajas (1966) showed that in accordance with the second of these two possibilities, the secretory granules¹ of juxtaglomerular epithelioid cells originate from the dilated, pinched-off rim of the innermost Golgi cistern (Fig. 5.1). Corresponding to this origin, also noted by Chandra et al. (1965), the nascent or so-called protogranules exhibit rhomboid or fusiform profiles. After stimulation of renin synthesis, rhomboid protogranules with a paracrystalline core are conspicuous (Fig. 5.3 A; Barajas and Latta 1965; Barajas 1966). In individuals without stimulation of the RAS, fusiform protogranules with an amorphous content predominate (Fig. 5.1; Taugner and Metz 1986). Besides, species differences have been observed not only in the electron density, but also in the shape of protogranules: in humans and monkeys they exhibit a polygonal shape, whereas in the rat protogranules tend to be more ovoid (Barajas 1966; Rosen and Tisher 1968).