Chromogranin A, the Major Catecholamine Storage Vesicle Soluble Protein

Chromogranin A (CgA), the major catecholamine storage vesicle (CSV) soluble protein, may index exocytotic sympathoadrenal secretion. To explore CgA in adrenergic tissues, we developed a radioimmunoassay for bovine CgA. Within adrenal medulla CSV, several minor chromogranins had similar amino acid compositions and peptide maps to that of CgA and also showed parallel, partial cross-reactivity in the CgA radioimmunoassay. CgA immunoreactivity represented 7 f 1% of total adrenal medulla cell protein and was localized to adrenal CSV, representing 46 f 2% of CSV soluble protein. In brain, there was 1000-fold less CgA than in adrenal medulla, with a widespead regional distribution (maximal in neocortex) and an unusual subcellular distribution (maximal in cytosol), both of which differ from reported catecholamine distribution. Brain chromogranin immunoreactivity also had a lower Stokes radius than adrenal CgA. Sympathetic nerve and serum had 6,000-fold and 30,000-fold less CgA than that in adrenal medulla. The results suggest a “family” of adrenal medulla chromogranins, similar structurally and immunologically. Adrenal medulla and brain ehromogranin differ in concentration, subcellular localization, and molecular size. Finally, CgA in serum may provide a useful tool for sympathoadrenal studies in intact organisms.