Abstract
Dynamic aspects of calcium action in the release of catecholamine were investigated in vitro, using perfused bovine adrenal glands and isolated chromaffin granules. The 45Ca which intruded into the chromaffin cells by acetylcholine stimulation was condensed in chromaffin granules and its localization was confined to the stroma of granules. The 45Ca added to isolated granule suspension in the presence of ATP-Mg++ also showed preferential binding to the stroma and this calcium showed a rapid exchange with unlabeled calcium in the medium.
Release of catecholamine from the chromaffin granules was observed in parallel with the binding of calcium to the stroma. Thus, stromal calcium plays an important role in the release of catecholamines.
The transient increase in free calcium concentration evoked by acetylcholine may trigger an increase of stromal calcium turnover. Under such a situation, the granules are brought to an activated, easily releasable state which would be the primary step in catecholamine secretion from the adrenal medullary cells.
