The membrane of catecholamine storage vesicles of adrenal medulla catecholamine fluxes and ATPase activity

Summary

1. A method of preparing isolated membranes of the catecholamine storing vesicles of the adrenal medulla is described. The membrane protein amounts to 23% of the total vesicular protein and still contains 0.1% of the catecholamine. 2. At 31‡C in the presence of ATP the membrane preparation accumulates catecholamine; in the absence of ATP, however, catecholamine is released into the medium. At 0‡C the catecholamine content of the membrane preparation remains unchanged, whether ATP is present or not, although a low catecholamine turnover is observed. 3. From the kinetics of the catecholamine turnover in the absence or presence of ATP a low ATP-independent catecholamine influx can be distinguished from a considerably higher ATP-dependent influx of catecholamine. 4. The catecholamine influx as well as the ATPase activity of the membrane preparation decreases with time; in contrast, the catecholamine efflux remains constant and is higher in the presence of ATP than in its absence. 5. Catecholamine is to a great extent accumulated within a membrane-enclosed space into newly formed particles; only a minor amount of the catecholamines is actually bound within the membrane.