Permeability of catecholamine granules.

The distribution of 14C-labeled adrenaline, ATP, urea, and EDTA in the intragranular and extra-granular water of chromaffin granules isolated from bovine adrenal glands has been measured and compared to the distribution of 3H2O. It has been found that the granule membrane is freely permeable to adrenaline, ATP and urea but impermeable to EDTA. Calculation of the rate of diffusion across the membrane shows that diffusion of adrenaline is not a limiting factor in the “active” uptake of this amine and that the site of the Mg2+-ATP-stimulated uptake does not appear to involve an activation of a transport mechanism across the granule membrane.