Abstract
There have been several reports that Mg++-activated ATPase is present in the catecholamine storage granules of the adrenal medulla (1-3) and that this ATPase may be linked in some way with the ATP-Mg++ stimulated uptake and release of catecholamine by isolated granules (4-9).
Recently, we found that the low concentration of Ca++ present in the incubation medium as a contaminant participated in the release of catecholamine from the granules stimulated by ATP and Mg++ (10). This finding is interesting in relation to the fact that acetylcholine or excess potassium causes the release of catecholamine from a perfused adrenal gland by promoting increased uptake of Ca++ into the cells (11-13).
This paper reports investigations on the effect of Ca++ on the Mg++-activated ATPase activity in isolated catecholamine storage granules from the adrenal medulla. The possible relationship of these results to the release of catecholamine from the granules is discussed.
