Exocytosis of secretory granules in the juxtaglomerular granular cells of kidneys

BACKGROUND: There is little agreement as to the secretory process of renin granules in juxtaglomerular granular cells (JG cells) of kidneys, although a large number of studies of the regulation of renin secretion have been reported. METHODS: The structural correlation between the stimuli and the secretory process was examined in mouse JG cells on renal cortical slices incubated with the beta-adrenergic agonist, isoproterenol; the loop diuretic, furocemide; the Ca2+ chelator, EGTA; and the actin filament-disrupting agent, cytochalasin B. RESULTS AND CONCLUSIONS: Treatment with isoproterenol (10(-5)-10(-3) M) or furocemide (10(-3) M) in Ca(2+)-containing medium did not significantly affect the ultrastructure of JG cells. In slices incubated with isoproterenol or furocemide in the Ca(2+)-free medium, JG cells occasionally contained a few electron-lucent granules at the cell periphery in addition to the electron-dense mature granules observed in the control slices. On rare occasions, the JG cells displayed omega-shaped cavities with electron-lucent matrices, a feature similar to the contents of electron-lucent granules. Cytochalasin B markedly promoted the effects of these stimulants in Ca(2+)-free medium. These findings suggest that participation of actin filament disassembly in the exocytotic process of the mature granules in JG cells.