Lysis of chromaffin granules by phospholipase A2-treated plasma membranes. A cell-free model for exocytosis in adrenal medulla.

The possible involvement of phospholipase A2 (PLA2) in the release of catecholamines was examined in a cell-free model system, using isolated chromaffin granules and plasma membranes of adrenal medulla cells. Plasma membranes treated with PLA2 in the presence of Ca2+ caused lysis of chromaffin granules which was also dependent on Ca2+. This finding suggests that Ca2+ acts in two steps of exocytosis, namely in the transformation of plasma membranes into a lytic form by PLA2 and in the interaction of chromaffin granules with plasma membranes. These findings show good agreement with recently reported findings in leaky adrenal medulla cells, and suggest the involvement of PLA2 in the release of catecholamines.