The fate of the chromaffin granule during catecholamine release from the adrenal medulla—II

Subcellular fractions obtained from bovine adrenal medullae stimulated to secrete catecholamines were compared with corresponding fractions from unstimulated medullae. Stimulation (with acetylcholine) caused a fall in the catecholamines and protein in the ‘crude granule fractionrs, but no change in the phospholipid or cholesterol. Further resolution of the crude granule fraction by density gradient centrifugation revealed a redistribution of the phospholipid and cholesterol after stimulation from the denser to the lighter layers. The results are interpreted to mean that the membranes of the chromaffin granules remain in the chromaffin cells after catecholamine secretion as discrete particles with reduced specific gravity. Probably these particles are the electron-translucent granules observed by electron microscopy in stimulated chromaffin cells.